Mike I have a 1980, 13ft Boler
and I have a Colman 1200 (about 100 lbs)on the roof with no extra support system.
I did not install it and the trailer came from FL and is now in Maine so it has been on the trailer with no ill effects for many miles.
There is little sag in roof, and while inquireing about tradeing the 1200 in for a 700 series. but people at RV dealership said the weight
differance would be only 4lbs and after inspecting roof of Boler
they said there is no problem or stress cracks and as long as there are no leaks
where water sits around seal there is no problem.
They also stated that any trailer built in Canada or U.S built after the early 70's had to be built strong enough to hanlde an AC unit on roof.
Don't know if it is true or not but mine is doing just fine.
Gerry the canoebuilder