the 2008, did they say they drove it on salty roads- or are you assuming?
in either case a quick look under will tell.
I grew up in Canada and have had cars rust our from under me in just a few years...
now in AZ even my 40 and 50 year old cars are completely clean underneath and rust free.
Get under and look.
The rental will also need a good looking at, rental drivers may not be so great about controlling speed with engine braking/ gear selection so the brakes could be affected- any signs of pedal pulsing when brakes applied?
as for the fridge, dometic as much as says the fridge will be ok if the passenger is ok..so a slight tilt is fine.
on the rental are the finish and materials for the interior as nice? or "industrial grade"
mike