'Beemerphile' hit the nail on the head - If your converter has 'smart' charging, then you can and should leave it hooked up to power all the time. It will keep your batteries charged, without over-charging or 'cooking' them. If your converter does not have such...Well, if it was me, that'd be the next thing on the 'upgrade' list for the RV, hehe. :)
Even if your converter has smart charging and you chose to leave it hooked up, I'd still check the batteries maybe once a month, make sure the water levels look OK, and add more as needed. A 'smart' charging system should prevent the batteries from having all their water 'cooked' out, but I'd still keep an eye on water levels to be sure.
I have always kept our RVs parked at our house, and plugged up to AC power year-round (I installed a 30 amp outlet at house for this very reason). Keeps batteries fresh and ready to go, without having to do much with them except checking the water levels every so often.
