The maximum power voltage (Vmp on panel label)
is not too important if you are willing to invest in
the proper charge controller. However, the best
controllers can be expensive. A good example is
the Blue Sky Solar Boost 1524iX (~$200). Once
you decide on which controller you are going to use
you can pick a panel that fits in the input
parameters of the chosen controller. A 230 Watt
panel seems a bit large if your power requirements
are not too high.
For single panel installations I would not mount the
panel to the trailer. In my experience it is best to
park the trailer in the shade and have the panel in
a sunny area. Of course there will be a voltage
drop in the wire connecting to the panel. So it
can be advantageous to have a panel of a little
higher voltage/power output so that the controller has
plenty to work with. Also, at a higher voltage there
is less power loss in the connecting wire than with
a lower voltage.
Limiting your power needs is always a good strategy.
One of the best things to do when starting a solar
installation is to figure out what your power needs are
and then design the system accordingly.
Two 12v batteries are not necessary. One good one
can be sufficient and save towing weight
Finally, important considerations are:
How much power will you use each day.
The period you will be using the trailer off grid.
What the capacity of your battery is.
The depth of your pockets.
How fit are you to be able to move a panel around.
Does your tow vehicle charge the battery when towing.
I hope your installation goes well. The fewer generators
I hear in a campground the happier my camping experience.