Seriously, if you can take it to where it remains frozen all winter and doesn't ever rain, just do it. Living in a climate where it rains and freezes and having your RV exposed to that will make you wish you spent $30,000 on a roof after you spent $60,000 on a motorhome really fast.
Best solution might be some indoor outdoor carpet under plywood next to your roof with two by tens tapered to the center screwed from underneath and on edge every so often down the length of your rig and extending out over the sides a few inches then cover it all with double "truck tarps".
I saw one done like this once, and he hung filled milk jugs from the eyelets on bungee cords and they swung a bit in the breeze but kept the whole thing open to the air quite well.
