Jim:

A 10 watt solar panel is only good for maintaining a charge on your
batteries, not recharging in a short time. A 10 watt panel doesn't need a
controller. A rule of thumb is that if the charging current is less than 2%
of the amphour capacity of your batteries, then you don't need a charger.
For even a single group 27 battery you will be below this threshold for a 10
watt panel.

As you note, for a 3-4 day cruise it isn't worth installing a big solar
array to keep your batteries charged up. It would take 100-200 watts to
begin to keep up with refrigeration and other demands of extended cruising.

I would first install a high output alternator and a good regulator- Balmar
sells a package for $600 which will keep you going on a limited cruise
duration. You may have to run your engine for an hour or two each day, but
for occaisional use, it's ok.

David