Our rig had a Precision Temp RV-500 in it and we used it for years, but it did have some issues to keep it going. We now have the new RV-550, which is an amazing improvement. It is a much simpler design and has no circuit board to worry about, and doesn't have the issues we had before with the wind. We absolutely love it. I just got our rig out of storage, turned on the propane, flipped the switch and all the hot water I want (subject to supply, of course)
My truck camper has the old style tank unit and I hate adding that extra 50 pounds and waiting for the warm up, excess propane use, etc. I am spoiled. Love, love, love, the Precision Temp RV-550. It will cost you a bit more than the tank style, but if our experience is typical it will last much longer and save you some money on propane etc.