Custom iceboxes?

I understand how to tape a box and have done many although I have never seen the sawdust/epoxy combo to radius a corner before (might use that on later projects). I was referring to after I put the top on having to reach inside where it would be trickier, hence why I am considering making the back open-able as well. I would prefer the inside have the cloth as well instead of just a coating of epoxy.

You could glass the inside completely to include the inside top. Then, thicken some epoxy up with sander dust, or cabosil, then run a bead along the top edges of the sides and set the top down on the bead and add a little weight.  you could then tape the outer top to the sides to strengthen the bond.  I may be way off on what you are doing though since I am not 100% sure how you are going to build it in its entirety without seeing a drawing.  Looks like a fun project though.

You could glass the inside completely to include the inside top. Then, thicken some epoxy up with sander dust, or cabosil, then run a bead along the top edges of the sides and set the top down on the bead and add a little weight.  you could then tape the outer top to the sides to strengthen the bond.  I may be way off on what you are doing though since I am not 100% sure how you are going to build it in its entirety without seeing a drawing.  Looks like a fun project though.

I have considered just making the top half separately and completely fiberglassing both the top and bottom then using a thickened bead of epoxy between them and clamp together, then a layer on the outside to blend it in.. I don't really see a need for the sawdust approach in this specific case.
Right now I am more trying to figure out if I want a raised section of the box that is right behind my seat or just make it a flatter top maybe 2 inches above the top of the kayak (for easy of using crab pots).. I will get back to it shortly.

You may look into wood strip kayak construction.  They usually build the top and bottom separate and then stick them together.  You may find some ideas.  That often use the fillets that Craig mentioned for bulkheads.  Just another place to scavenge ideas.

Any more updates on this project and/or photos.  Very interested in seeing the finished project.

Would love to see some updated photos.

Thanks