Did I miss anyone suggesting a rental bike? Maybe the cost is prohibitive or the selection is limited? I did it once for a family vacation, we brought my partners bike and I rented. Next time I'll just rent both.

If I was traveling with a friend it's easier to keep an eye on things; if I was going solo I'd leave my personal bikes at home. Or like op mentioned maybe ship them to friends.

Road trip security for me means keeping a low profile. Keeping a clean and unassuming vehicle; a thief should be able to peer in and not be interested.
​​​​​​