Ice-box corner filet material under epoxy & glass…what to use..?

I am just getting ready to finish the final assembly of a rather large built in ice-box under the cockpit seating area of my catamaran and I was wondering what might work best for filleting/adding a small radius to the corners before laying some fiberglass tape to the seems with epoxy resin…? Brief description my ice-box is approximately 24 inches deep by 24 inches wide by 34 inches across. And is made out of 4 inch thick Styrofoam panels with a thin but solid layer of woven fiberglass & chopped strand matt combination bonded to one side with epoxy resin. I fitted the pieces (foam only) in place then removed them individually and glassed the interior portions while horizontal in my shop. The panels turned out really nice. Now I just want to install them into the ice-box frame and seal all the corners with a narrow stripe of fiberglass tape but I would like to lay a small radius of some kind of filler/fairing compound in the corners before doing so. I was going to us a polyurethane chalking but I thought it might be better to have a solid material to back up the glass. I am in Panama so my resources are limited. Is there anything wrong with using bondo or a similar material? I only plan on laying in a small radius so the tape will transition the corners smoothly. I am a novice with composites so any input is appreciated. I would like to avoid something that can absorb water and lower my ice-box efficiency.

Thanks

 

If this is just for waterproofing, bondo will work fine. After it cures, sand it and dewax it for better adhesion.

 

You should just make some filler for the fillet, sand when dry and lay your tapes on top. Use the same resin for the fillet with a suitable filler, maybe Q cells, micro balloons or similar.