over the yrs I have build many different types of deer blinds on trailers, and all sorts of trailers, from street legal one's to hay wagons and off road like/farm trailers
one thing I learned is, blinds can get VERY heavy very fast when building, making them weight way past what smaller trailer axles can handle, not to mention they can get very top heavy as well
I also highly recommend when building a blind on a trailer you build then on runners/skids, and attach good solid locations for adding tow straps/chains!
and don't forget to have lots of solid places to add tie down straps for if you plan to haul it on a road way or even off road, as again being top heavy they can get tricky fast in off camber or rough terrain!
and then you can always drag them, to locations or easier to just get off the trailer!
and if nothing else they tend to help stiffen up the blind!
Plus, keep in mind what ever roof material you use, if you tow it, a lot of wind will be on it and can peel off shingles or even tear off metal roof panels or likes, learned this the hard way once , didn;'t have a ratchet strap on ever roof panel and had one pull off, 3/4 of the way, doing damage to things, but never came off, but was close, had I not seen it happen, and pulled over, might have been different outcome, and I was only ona ropad with a 45 MPH speed limit, had I gone ona faster speed, I am sure it would have came off and maybe hit someone!
roof screw's in metal roof pulled right out!,. wind is a powerful things!
also some times its best to remove or not install windows till in location,a s if on a lot of uneven terrain when things flex, I have seen glass windows pop due to stress on them!
and LAST!
as for building in the back of a pickup truck, if you do this, make sure its legal to hunt out of , as in many places that would be illegal if its attached to the truck(I gather also even if trailer is still hitched up to truck too)
so some food for thought for anyone planning to build one!