I have used a tarp outside for 2 campers over the last 10 years, and it works good.
This is the first winter for the TM, and I just put a tarp over it, see pics.
The tarp is clearly stated as waterproof, and it is 10 mill thick.
Size is 20' x 35'. I watched a youtube video that showed how to fold over the
sides to the center, and then roll/fold it up. Then I carefully lifted/worked it
up to the back roof of the TM with an 8' stepladder. I used a padded push pole
to roll it forward over the TM from the stepladder. I put plastic milk crates on top of each shell,
under the tarp. The 2 light ropes hold it in place, due to the shell shape.
The TM door still opens after removing the rope on the curb side, and access
exists to the complete exterior and interior for any purpose. I prefer the open
camper position for storage. The bathroom vent fan(computer fan) is left on.
I may add a small inside fan to help with some mild ventilation.
The tarp usually shows some signs of wear after two years, and is replaced.
Good luck with your storage.
