Prodigy is the way to go, had it in my D2 and will be installing a new unit in the D3 next couple of weeks.
They are not a problem to install, just take your time and read the instructions thoroughly before installing, make sure you use the correct size wiring, protect your wire to the trailer plug and make all connections good ones.
I usually run a seperate hot wire for the trailer battery but I have just changed it on my new camper and have used the reverse light pin as I dont use it on this trailer
