I'm an out of the box kind of a guy so roll with me for a second. Home Depot sells small landscape trailers for less than a grand, I think somewhere around $500 but I could be wrong. You could mount a bike rack to the floor and a waterproof plastic box on the tongue for gear and parts. When I had a car USAA (my insurance company) told me that a trailer and its contents would be covered under my insurance policy. If you frequently transport bikes this would be a viable option. You could also install d-rings on the floor of the trailer and chain the hell out of your bikes to discourage theft and put a padlock on the hitch and hitch pin to prevent theft of the trailer.