We live in Eastern Washington, and get a lot of snow. I've had the same problem that you're experiencing. I turned off the fridge, raised the front of the RV up to get a good slope to the roof, and turned on the heat inside the RV. I ran a 110 volt plug in heater, and the propane furnace at the same time.
I didn't have any luck trying to slide or push the snow off of the roof. When the snow was gone, pulled in the slider. No damage, no leaking. I was concerned that the snow would allow water to run in around the slideout seals.