Some good ideas so far. I agree the permanent trickle charge is probably not a good idea unless it is the correct type that cannot overcharge your battery.
One solution is to use two 24 hr timers in series. Set the first to be ON for 2 hrs per day. That allows the second timer to cycle around every 12 days. Set the second timer to be on for 2 hrs and the charger is plugged in to that. So every 12 days you get 2 hrs charge on the battery. Arrange the settings on each timer to give you the minimum amount of charging that will keep you charged fully without killing the batteries from overcharging.