12v - 12v charger

I currently charge the (hard to remove) batteries in my ASH-26E with a
solar panel and charger installed on/in my trailer. During a contest,
the plane may not spend much time in the trailer during daylight hours,
but it does spend most nights in there.

The solution would be to use the solar panel to charge a battery in the
trailer, which would then be used to charge the glider overnight. Best
would be to use this system all the time with two chargers in the
trailer and a single cable to hook up to the glider.

So... does anyone know of a charger that will accept 12v input to
charge a 12v/18ah SLA battery? I've found some charger chip
application notes, but I really don't want to build one of these.

Thanks,

-Tom