Originally Posted by Ian G.
It is not just the 100 lb static load, consider the dynamic load every time you hit a bump. I would recommend using supports down the wall to support the beams across the roof to the carry the load right down to the floor. The walls are just 1/8" thick fiberglass and not designed to carry vertical load, they will start to bow out from the weight.
Those trailers were not normally fitted with roof A/C at the time...
The walls are already supported by the furniture, and what I described was the standard endorsed solution at the time the OPs trailer was built for those who wanted a roof mount.
You are correct that the Scamp 13 was lighter and thinner thirty years ago, even the frames were lighter gauge and the axles were 1200# instead of 2200#.
Still many trailers were successfully fitted in this way and have endured over time.
I would prefer the fiberglass application on the ceiling mentioned earlier.
Ed Smith had Scamp install roof air recently and using this method and it is excellent with a factory look and finish. No additional wall support was used or needed.