sounds like you could take some 1/2" pipe and cut spacers the same length as the thickness of your plywood. drill holes through the plywood big enough for the pipe to sit in. then drill holes in the frame small enough for the bolt to fit through and the spacer to sit on. then mount your smoker to the trailer and it will sit on the spacers and not crush the plywood but be tight to the trailer.
No change at all since it's mandatory to have a trailer registered in this country. And it's way easier to modify existing one, it's almost impossible to build one and get it to comply with every EC regulation etc etc
Frank that's a good idea, although I'm not that worried about the plywood (it's already a bit rotten). I'm just worried I have nothing strong enough on the trailer frame to mount to.