I have had up to 2 feet of snow on my TT roof which I removed after the storms with a plastic snow rake. The snow was dry and so it was light. Not sure I would want that amount of wet snow up there though. I clean any amount of snow if the snow event is followed by mild weather or rain. Freeze/thaw cycles and wet weather are also a concern.
The local RV dealers were not worried about it, though--I do not recall them ever shoveling off a roof.
The only issue that I ever had was tearing the TT cover when the rake caught a wrinkle........ I don't use covers any more. LOL.