Rob,
If you just want the solar panels to trickle charge your batteries
rather than supply appreciable amounts of power the task is pretty
easy. I used solar panels to keep the batteries of my sailboat charged
up for use on weekends. The boat was kept at a mooring and most
weekends the engine was not run long enough to fully charge the
batteries. For top off or charge maintenance installations fitting a
solar panel is simple. It ain't brain surgery.

First, note the size of the battery bank that you want to keep topped
up. Assume that the battery will lose about 1% of its charge per day.
This amount may vary depending on the age and quality of the battery
but 1% is a good estimate. If you have a 200 amp hour battery, the
solar panel will have to provide at least 2 amp hours per day to keep a
fully charged battery topped up.

Second, most solar panel experts maintain that a typical solar panel at
a moderate latitude, i.e. most of the continental US, will provide full
electrical output for only six hours a day. That means that on a good
day you will need a solar panel capable of putting out .333 amps to
keep the battery topped up. Given the fact that  there are occasional
clouds, a 5 watt, 12v. solar panel should do the job nicely. These are
typically sold in auto and boating stores as trickle charging batteries
and cost about $100 or less. While the nominal voltage of the battery
is 12 v. most put out between 15 to 18 volts. For safety's sake you
might want to put a diode in the line from the charger to the battery.
This will prevent a reverse flow of electricity from battery to the
solar panel if there is no panel output or a short circuit. Most solar
panels already either contain a built in diode or will not allow a
reverse flow of electricity.

Third, if the maximum output of the solar panel is less than 5% of the
capacity of the battery, you do not need a charge controller, although
putting one in the line wouldn't hurt. But for a battery and a solar
panel in this range it is just an added expense. Your 200 amp hr
battery could use up to a 10 watt solar panel with no more protection
than the in line diode.

You will have to scale these figures up or down to the size solar panel
for the batteries that you have.

Small solar panels in the under 30 watt range are sold in just about
every boating store. You can save about 20% by buying on the internet.
Just do a google search for solar panels and you will find more
information than you want to know.

Larry Z

Bob and Larry:

While I mostly agree with Larry's recommendations, I think that his rule of
thumb of 5% for not needing a charge controller is about double too high. I
had an RV with 200 amp hours of battery capacity. I left a 32 watt solar
panel hooked up continuously for several months. Admitedly this was in
southern California with abundant sunshine. While it probably didn't hurt
the batteries, it sure used some water. I had to add water every other month
to keep the level up.

A $50 charge controller will solve that problem. You don't need a MPPT
controller just a cheap Morningstar or something similar.

David