I don't know if there's a 'real' rule, but I remove snow from mine as often as possible. Here in South Jersey, we got about 18" saturday & expecting around that much tonight. I spent my lunch hour at storage sweeping the snow from my roof. It seems the snow was shielding an inch of ice. Once I removed the snow, the ice melted in 30 mins. Now, my roof is all clear for round 2!
Whatever you decide, please think safety first! My rig has a fiberglass roof & it was very very slippery
2012 Thor Astoria 36MQ
Butter Toffee on Toasted Almond
'96 Cherokee toad Tim, Dar & our black Lab "Chase"