The built in 12v I had in a used sleeper was DOA, so I got a Haier from Walmart for around $80? and put it in the same cabinet. The Star Class sleeper is on air, but the cab is not, so there is still some rough riding on city and suburban streets. The frig lasted about a year, then died. I am certain it died from vibration- it could even be a simple fix, but I have not bothered to pull it out and look.
I think to be successful for any length of time, you would need to mount it on pliable rubber of some sort...I am convinced now that the best alternative is a 120v cooler with a decent fan to keep liquids cool, and perhaps a sandwich for a short time. I had great luck with a small "Koolatron" that I used to keep on the floor between the seats- it did a good job and I left it behind with an ex-girlfriend. For the money you save, you could get a larger one and put it in the cabinet space designed for the 12v fridge. I think they sell for around $115- less at a Walmart of course.