Trailer box materials and construction

[Tiny Turnip]

I have a Christmas tree canoe trailer and have twice built a simple ply box under the lowest rung for gear storage. I've used 1/2 inch and 3/4 inch WBP ply, 3 coats of cellulose paint, and twice the bottom has rotted out in under 2 years. The box lids lap over with a downstand, and the hinges are fully protected with a rubber strip, sealed and tacked down.

I'm going to pull it out of the brambles and have another go. Am I on a hiding to nothing with WBP ply? (I suspect a number of the local timber merchants bought in some poor quality stuff at the time, in fact.) I'd rather keep the build quick, easy and strong - don't really want to get involved in aluminium fabrication, but I would consider a plastic or composite board if anyone knows of something suitable available in the UK.

OR would a couple of coats of polyester resin be a better bet?

And any ideas for a simple but effective hinge and lid details?

Here's a picture of the trailer sitting in the brambles to give an idea of what I'm at. (which have only grown up this year -the rot happened long before the brambles grew)

Thanks.

 

[bajansailor]

If you 'fill up' the box, typically how much weight would you put in it?
And how much weight would the roof of the box have to cope with, re things stowed / lashed there under the 'branches' of the 'trees'?

Would it be feasible to build a box out of say 1/2" or 3/4" thick foam board that is covered in arborite / formica both sides, perhaps with 2" x 2" timbers in the corners for attaching fasteners to? And maybe build a lid out of the same material?
You could even put some glass tape with epoxy over the corner joints if need be.

 

[Tiny Turnip]

If you 'fill up' the box, typically how much weight would you put in it?
And how much weight would the roof of the box have to cope with, re things stowed / lashed there under the 'branches' of the 'trees'?

Would it be feasible to build a box out of say 1/2" or 3/4" thick foam board that is covered in arborite / formica both sides, perhaps with 2" x 2" timbers in the corners for attaching fasteners to? And maybe build a lid out of the same material?
You could even put some glass tape with epoxy over the corner joints if need be.

Thanks for the reply. Sticking a finger in the air, I might put a couple of hundred kilos of heavy camping gear in the box - nothing to stress the bottom panel - there is a steel cross member mid span under as well.

I don't lash anything on top of the box - the lowest branches usually take the main trimaran hull just above the box top. I might stand a bicycle upright in the middle, tied to the frame, but the centre spine of the box between the hinges is well supported.

The material you describe and framing / corner taping is exactly the approach I was thinking of, but I can't find a similar material / don't know what brand name to search for in the uk.

 

[Tiny Turnip]

The box lids might get someone leaning or possibly sitting on them every now and then.

 

[bajansailor]

Dare I say it, but the foam of choice that various boatbuilders / repairers here are using most enthusiastically now instead of plywood is the standard panels (with laminate on each side) used for kitchen cabinets - but make sure that it has a foam core, and not chipboard!
I built a ramp out of this board (3/4" thick) eight years ago for a friend so that he could wheel himself up to his front door - I added a layer of stitchmat with epoxy on the top surface, but nothing on the bottom surface, and it has had heavy usage ever since from his wheelchair and heavy people walking up it, and it is still as good as new.
Maybe IKEA might sell these types of panels? We can buy them here in 8' x 4' sizes, but I don't know the brand name.

 

[Rumars]

The cheap option is using phenolic resin coated plywood with epoxy sealed and painted edges. This is standard in trailers, it comes with a smooth or textured surface, usually a dark brown. The important part is properly sealing and painting the edges and fastener holes (epoxy resin + paint). The ply is available everywhere.
The more expensive option is a polypropylene honeycomb sandwich panel. The skins are aluminium or fiberglass, either fused or bonded. The panels are joined mechanicly with rivets or screws, glued, or welded. The seller normally also offers the joining solution. You need to choose the appropriate thickness for your application.
Another option is foam-fiberglass/carbon sandwich panels.

If you want sandwich panels at low price make the box out of PUR/PIR foam laminated with fiberglass in polyester resin. If esthetics are not really important you just gelcoat over it and don't sand at all.

 

[kapnD]

Try cutting some slope into the top of the box, so that water will drain to the outside edges.

 

[Tiny Turnip]

Many thanks all for taking the time to help - much appreciated!

Dare I say it, but the foam of choice that various boatbuilders / repairers here are using most enthusiastically now instead of plywood is the standard panels (with laminate on each side) used for kitchen cabinets - but make sure that it has a foam core, and not chipboard!
I built a ramp out of this board (3/4" thick) eight years ago for a friend so that he could wheel himself up to his front door - I added a layer of stitchmat with epoxy on the top surface, but nothing on the bottom surface, and it has had heavy usage ever since from his wheelchair and heavy people walking up it, and it is still as good as new.
Maybe IKEA might sell these types of panels? We can buy them here in 8' x 4' sizes, but I don't know the brand name.

This is exactly what I had in mind, Bajansailor.. The nearest I had found was foamed PU sheet, (as used for building fascias) but I couldn't find it any thicker than 10mm, which I don't think would be strong enough and is a bit too bendy - and still double the price of ply.

The cheap option is using phenolic resin coated plywood with epoxy sealed and painted edges. This is standard in trailers, it comes with a smooth or textured surface, usually a dark brown. The important part is properly sealing and painting the edges and fastener holes (epoxy resin + paint). The ply is available everywhere.
The more expensive option is a polypropylene honeycomb sandwich panel. The skins are aluminium or fiberglass, either fused or bonded. The panels are joined mechanicly with rivets or screws, glued, or welded. The seller normally also offers the joining solution. You need to choose the appropriate thickness for your application.
Another option is foam-fiberglass/carbon sandwich panels.

If you want sandwich panels at low price make the box out of PUR/PIR foam laminated with fiberglass in polyester resin. If esthetics are not really important you just gelcoat over it and don't sand at all.

Thanks Rumars - including the word 'sandwich' in my searches has made a lot of difference! I've found a couple of companies which will do custom size grp/PUR/PIR sandwich panels. I think the answer is going to be the phenolic ply though - in truth I had not bothered to look for it as I assumed it would be way more expensive than wbp, but I've looked this afternoon and its not much dearer. And I'll seal all the edges prior to assembly.

Try cutting some slope into the top of the box, so that water will drain to the outside edges.

Thanks Kapn - there is actually more fall to the lids already than there looks, and I wanted to maximumise the volume and height of the box, so I'm unwilling to slope it too much more.

Best

TT

 

[Rumars]

Put coats of epoxy wet on wet until on all the edges until the wood does not suck it anymore, then three more coats also wet on wet. Same for any screwholes, let them drink epoxy. Then paint with exterior oil paint to protect the epoxy from UV. Assembly the box after sealing and painting.
If you get bad ply and have holes in the edges (missing veneers) fill them with thickened epoxy.

 

[Tiny Turnip]

Thanks Rumars. That all sounds good.​