I have seen RVs with 4 inches of snow on the roof and toppers. The toppers had no problem rolling off all the snow. On another occasion one of my toppers rolled off a half inch solid sheet of ice with no problem. I have seen people on top of their RVs sweeping off snow hoping they did not slip off. There should be no more reason to shovel snow than a heavy rain.
However, some states have laws that make a vehicle liable for any thing coming off the top and damaging another vehicle following behind. For that reason you may need to check the snow load on top.
Bob & Joan Alexander, 2010 Tiffin Phaeton 36 QSH, 2013 Jeep Wrangler (toad)
Lobo & Juniper (woof, woof)