I use a Battery Minder Plus. This unit has a pulse desulfate mod. The Battery Tenders are good however most do not have the desulfate mode. Desulfating your deep cell battery is the key to longevity.
While I do have a Progressive Dynamics converter which has high voltage desulfate, I still use the VDC Electronics Battery Minder when the camper is sitting between trips.
http://batteryminders.com/12-volt-maintenance-charger-desulfator-1500 I have the prior model, this newer one is even temperature compensated.
I have 5 of these, have 1 on the truck, tractor, lawn mower, SIL's boat battery and the camper.
Desulfating is a big deal. Search the web for the model number you are looking for. They sell for less through sales outlets then factory direct.
Hope this helps
John