The charger is not as important as how you maintain the batteries. As was suggested, connect them in series and any decent 12-volt charger with a deep-cycle setting will do. I have a couple of chargers I bought from Sears. I also have a Schumacher I bought at an auto store. Make sure that the batteries are fully charged when you put the unit away after a trip. If it is going to be stored more than a couple of weeks, put the batteries on a trickle charger. Check the electrolyte level often. I check mine once a month. I also keep a desulfator connected to my golf carts when they are in storage.
Miles