Ideal Gas Tank Installation?

First rule seems to be for installation - don't foam in the tank. So if my 70gal rectangular aluminium tank, about 6' long by 18" deep, rests on longitudinal placed poly plastic tubes - would that work well?

My idea is that tubes at say 1' centres would squash into soft bearings with fore/ aft drainage runs and good ventilation.
But there is one other facility which this would provide.
The tank is midships under removable floorboards with its aft wall being the front wall of the (large gas) engine compartment.
Now, I have been very concerned by the manufacturers pitifully sized engine vents - proper adequate replacement sizes would be very large on the hull sides. (not for bilge gas removal - engine air intake)
So, how about sufficient drainage holes in the base of the tank compartment wall for water - and sufficient upper holes to vent the engines through the tank compartment floorboards? Debris shrouds could easily be constructed across the tank floor cutouts shaped to avoid non trip.
If the carburettor noise path has to travel through a bulhead, along the tank and past floor shrouds, then hopefully it shouldn't be too noticeable.

The other answer would be huge side hull vents allowing salt, water etc in.
Any thoughts on my two ideas, plastic tubes bearers and internal engine vent?

 

The only way to install an aluminum tank, IMO, is to have welded-on angle and bolt through that to mount. In thirty years when the bolt holes show corrosion, move them over a bit. Complete air circulation is the path to longevity for aluminum tanks. I feel like the plastic pipe is a weak link and will allow movement.

 

If the fuel tank and engine are open to each other I would close that off as a fire stop and vent each space independently. Is it a wood boat or fiberglass? You need to allow for water to flow to the transom and you can vent top side say port side and exhaust starboard side using power vents. What is your engine source? Sparks and heat, need to be seperated from fuel.
I agree with Mark 777 have angle welded on and bolt that down. Gas is heavy and must be strongly bolted down

 

FWIW:

I clean hundreds of fuel tanks, equipment, underground, vehicles, boats, etc. and my professional recommendation would be:

I would set the tank on a platform and strap it down. Lugs or cleats welded to the tank are good, but you need to support the tank and it's shock load. I see tanks imbedded in foam and almost aways there is dampness. When I see a tank strapped in place it is dry. Of course I am talking aluminum tanks here.

Poly tanks have their place, but not in my boats.


El Sea/L.C.

Suckin Sludge & Havin a Gas

 

Thank you gents.
I take note of firewall - and will prevent newspaper reporting another tragedy.

Have to devise some flametrapped tubes to drain the aft wall of the gas tank compartment to the bilge in the engine compartment . . .