Remove wheels or move on a regular basis to avoid flat spots on the tyres
Have the dandy low at the draw bar end for water to run off without it going on the door bottom
Put a foot ball under the cover to stop rain sitting on the top
If the transit cover is old put a cheap tarp under it in case it leaks over winter
Dont leave any food in it to attract vermin
Dont leave any thing dangling down on the out side for mice to climb up,they can get anywhere but a flat upright surface is harder to climb than a dangling string.