Original Message

They company is liable for your accidents when driving for company business.  They'd rather pay for your cheap rental car repairs than repairs on your expensive personal vehicle or more expensive RV. They can't provide a car for every local business drive, though. That's why AMC has the mileage limit and tries to limit your rental upgrades.  They don't mind if you drive, just don't put the company at risk.

If you have a valid reason for exception to the policy, they can and do waive it.  RV isn't going to make the cut though.