I spent a few months in the Florida keys with my Rover last year. It got completely rusted up. the forks, chain, brake disks, and the rear cartridge. I think if you are going to store it outside you'll just have to accept rust.

I recently just worked through this problem with my RadRover.  Rad support was great about it. They first sent a controller and when that didn't fic the problem they sent a new main wiring harness and that did fix the issue and the bike turns on just fine now. If I were you I'd pop the controller off the bike that isn't working and connect it to the working bike. If the bike powers up you now know that both the display and the controller are good so you've narrowed it down to the wiring. They covered mine under warranty but if you are out of warranty the harness was just $30.