I would not use a tarp, you will trap moisture. The frame and tarp roof idea might work okay depending on wind or snow.
I use an Adco cover for winter storage only. It breathes and is strapped under the trailer. I can get 4 feet or more of snow on that roof, and I don't like the melting snow getting into all the pipes, A/C unit, fridge vent, vent covers, ect. and it also keeps a lot of dirt / leaves / debris off the top of my trailer. In the past I've had damage from ice without a cover installed, has ripped off pieces of the roof membrane during a thaw freeze cycle. The cover has completely stopped that. It also comes out much cleaner in the spring again.
