I am beginning to think the best route may be to NOT mount the antenna permanently. I can glue the metal plate from a junction box to the roof and walk the magnetic mount antenna up there when needed, but just leave the cable loose for temporary use. This will mean another step in my setup and break down for camp, but I'm hoping it won't be necessary in locations other than those I plan to use in the state parks of New Mexico. If this doesn't work I will still have the option to install the antenna and route the cable permanently.
Thanks for the suggestions,
Glenn