A lot of people seem to be having good luck with the hard wired units purchased on eBay and Amazon. If you are looking for a good system other than those
Rearview Safety seems to have good systems that are sold piecemeal or as complete systems. They did have a couple vehicle rated hard drives to record video from up to 4 vehicle mounted cameras. They also had a couple systems that record G Force data and GPS in case of an accident. These systems are made for use on any vehicle from the family car or RV up to commercial vehicles and tractor trailers.
They are still much cheaper than the ones sold by the RV dealers.