Do you plan on leaving this hooked up to your truck while you are cooking? I'm just curious because of the question about having table space. I would wonder about having a hinged table that would cover your toolbox and wood storage, and flip forward when in use to cover over the tongue area. I've had one too many whacks on the shin from walking into a trailer hitch, and it would direct flow around it. If you shaped the bottom of the table/work surface right, when it was flipped back not in use, it could cover your toolbox and storage areas, and a little slope would help shed water. Just thinking out loud here.
I might have to come inspect it when you start testing it. I think you're about 30 miles north of me.