keeping car trailer batt. charged

what are you doing to keep your batt in car trailer charged up;;I have one batt I use for wrench that I have to raise and lower my ramp door;;;2nd batt is used to operate wrench to pull car in and out of trailer;;also operates my hyd jack that raises trailer to hook and unhook trailer from truck and used to start generator;;][ohman 4000 gen set]seems like every time I turn around I need to drag battery charger into trailer and charge batterys;;was thinking mounting 2 solor panels on top of trailer and hook up to batterys permety to charge batterys and maintain them so girlfriend got my 2 Schumacher SP-400'S;;IN INSTALL BOOK SAYS THAT ONLY MAINTAIN BATTERY AND WON'T CHARGE THEM AND CAN'T BE MOUNTED OUTSIDE[not water proof]
So what are everyone doing to solve this batt dead issue?is there a affordable solor panel that I can mount on top of trailer permently and leave hooked to batt 24-7 that will keep batt at full charge and recharge them back to full charge after I use them and they start getting weak?

 

A quick internet search and I found this on Amazon. It's fully weatherproof, and cheap.

http://www.amazon.com/Lowest-Price-...570&sr=8-15&keywords=solar+battery+charger+rv

 

I went to Tractor Supply

I went to tractor supply and bought a solar panel, about a foot square. I don't remember if it said it was waterproof, but it has worked great for three years outside in all types of weather.