Not sure if the intent is to rent the RV in MA and drive to Alaska or just to rent in Alaska. If the intent is to rent in Alaska, there are other options (Great Alaska Holidays, ABC, etc).
I know there are likely hundreds of success stories for renting of private RV's, but I've dealt with two disputes (one from the owner / lessor side, one from the renter / lessee side) using similar services and my clients (on either side) had nothing good to say about their experience.
The point raised regarding a mechanical issue is quite valid...lots of road miles in AK that aren't close to metro areas and tow services.
CRL
My RV is a 1946 PA-12
Back in the GWN