How would you waterproof plywood?

[hank4elk]

Try marine grade plywood. Then paint with something that will seal it. The edges will be a problem because water just wants to get in between those layers.

Edges need to be closed or sealed for sure. Filler on edges & seal several times before painting or epoxy or varathane....

 

[Bambistew]

I made a few "tool boxes" for truck beds, and with proper maintenance, they lasted about 7-8 years I used them. I used marine plywood, sealed with linseed oil and Thompson's water seal or the like... It won't last forever, but it will last a long time. They were in the bed of a truck 365 days a year. I reapplied linseed and Thompsons every year.

 

[mplane72]

Didn't read all responses but short answer is you don't. Best option IMO is fiberglass and resin.