“I’m pretty sure the wall and ceiling supports are also 2×2 square metal tubing”,I wouldn’t hold my breath!Ask them what the frame is made from.ask what the roof is made from those top hat roof bows aren’t that strong.also have them put that green ext.ply on the floor.I have a trailer that after 4 years is rotting by the back door because the wet roads and mud get up under the trailer and on to the plywood underside and has caused rot.You can also contact the manufactuer about what you want to do and ask them if it will be strong enough for your plans.If they don’t know the dealer won’t.you can also just have the 12″O.C in the area of your hood if needed.