When it comes to an enclosed trailer, it is never big enough! You will always find more things to put in it!
Your limitation will be the total length. Most states are around 65' to 70'. Use an equalizing hitch and sway bar an you will be fine. Because of the wheelbase, a motorhome is one of the most stable vehicles to tow with. Believe it or not, the longer the trailer, the easyer it is to back up.
As far as storage when you are not using it, if you have room at your house, keep it there. They make great storage for your patio furniture in the winter too!.
When you do keep it in storage, BE SURE to lock the heck out of it! Thieves are everywhere and they don't care about you or your stuff.
Those nice latches that the lock go through on the doors; they are just blind rivets. You can pop them off with a screwdriver. Replace them with round head lag bolts and lock nuts on the inside. Those nice tongue locks; hit them with a sledge hammer and they break right off! Had this happen to me.
To secure, use a good lock on the moveable part of the tongue latch, a sealed tongue lock and most important, Chain the wheels together on one side. Locks won't stop a thief, many locks will slow them down or make them move on to the next target. Don't scrimp on the door locks either!
Hope this helps!
Terry