I installed Barker Auto-Drains on my old fiver-loved them and miss them tremendously-they installed over the existing dump valve so no messing with plumbing-and if one did fail you could open it up and manually dump(I did have one fail-I tried closing it when there was ice in it and chewed up a gear-had parts overnighted to me for quick repair.
I've been thinking about the Valterra for the Carriage because I like the remote control panel and want to have a set of switches in my wet compartment as well as at the main control panel in the coach-on of my principal reasons for going to electric valves(besides the sticky remote cables) was to be able to open and close my grey valves at will from inside the coach.