I tried storing outside in March and found the command stick on's were melting off the wall so I went indoors. I did like having almost 24/7 access to go tinker but I worried about it being stolen even though they had cameras. Sunbrella® covers protect somewhat but they still recommend cracking
windows and vents when in sun and they are heavy so you would need several people to help put it on.
In order of cost:
1) Private indoor storage garage at self store locations - very pricey, need garage door lock. You may or may not have 24/7 access but you will have a lot of access. You will have power so you can keep batteries charged.
2) There is indoor storage in large warehouses - pricey but you don't need a lock and you will probably only have limited access so you may not be able to go there to do any hanging out or working on your trailer. They will usually charge your batteries every now and then for an extra charge.
3) Share a private indoor storage garage big enough for two at a self store location - A bit cheaper. You will need a lock for the garage door. You may or may not have 24/7 access but you will have a lot of access. Will also have power so you can keep batteries charged.
4) Look on craigslist to see if someone has a garage to rent that it will fit or a backyard with shade - Cheaper and you may or many not need a lock and may or many not have 24/7 access. You may or may not have power to keep batteries charged.
4) Outdoor storage areas - least expensive. May or may not have 24/7 access and you will definitely need layers of locks even with security cameras at the storage location, cover, wheel covers (although my friend always finds hers get stolen). No power to charge batteries.