Future firewood build

I haven't posted here for a while. I think some of you might know about what I'm asking here. I want to add a box to my folding flatbed trailer so it can store my lawn tractor out of the rain. Also to keep chainsaws and stuff safer on the road without a lot of tarps & tiedowns. I would like to be able to toss it in the fireplace some day and IIRC there are restrictions on what I can burn in NY state. Pressure treated lumber is definitely out, painted is out too I think. Plywood may be out depending on the glue, and cadmium or zinc fasteners would be out because I shouldn't burn them.
I'm thinking linseed oil might be enough protection if there are a few of coats, and it's from a plant so it's basically firewood already. I may need the plywood to keep it lightweight enough. I think Elmer's type glue would help, I like gorilla glue but don't know if it's a crime to burn it.
Ironically the usual thing is to take the stuff I shouldn't burn to a municipal waste facility where it will likely end up burning at a garbage-to-energy plant that's usually upwind from me.
I'm open to common sense when available, and I guess if a wood structure rots & burns enough times it will be just as eco-unfriendly as making the whole thing with epoxy.
The question is how long will last after how much work to build it. Even an all metal one might have value when scrapped.
Any thought or suggestions? The size is roughly 4x8 and as tall as necessary. I can overhang the wheels & tongue a little. I plan to do 65 mph when I travel, so it can't be flimsy.
I chose this picture from a thumbnail, the trailer as-is is on the left. Extra stuff shown is for your entertainment only.

For the time being I made a lightweight frame out of poplar and hurricane ties.  I sized it so a tarp I already had could fit nicely.  It's held down by eye-screws and upside down coathooks that were 4 for $10.
The trick was to make "hospital corners" with the folds put where they don't scoop air at high speed.
It made a 300 mile round trip up to 65 mph without a problem, and the wood is still fireplace-ready.

Here's some pics of the frame and stuff.  The bottom is 2x10 in the front and rear gate with 3/4 plywood sides and red oak 1x2 on the top edge.  The front has a 2x2 hole in it for a makeshift receiver hitch.  I made a wood carrier for a motorcycle battery and the winch controls.  The bix frame is 1x2 poplar.  It costs more than half what red oak would cost so I saved money and got nice wood but it is softer than I expected.  The hurricane ties are $1 for the doubles and $.50 for the small ones.  They have #10x3/4 sheet metal screws in most places.  The ATV is about the same height as the mower wing & steering wheel.  Inside clearance is 48" but the supertrapp is higher than that so I need to re-position the exhaust or take the supertrapp off it to fit the mower.