Doug,
I pretty much did the same thing.
Using 1/2 ply made it 9ft x 3ft. Single lid that runs on 4 x 2 inch rubber wheels.
Lift the back edge of the lid 2 inches and just give it a push and it opens right up. Also give it a push and it closes and seals all round so no matter what the weather or driving conditions everything inside stays dry.
Layer of 135gm glass with epoxy on the outside with a coat of polyurethene. So easy to open and close while the bot is still on the trailer.

Did what I wanted.

Regards,
Phill

I know that the voices in my head aint real,
but they have some pretty good ideas.
There is no such thing as a quick fix and I've never had free lunch!