Thank you, Eric, this is a good start knowing that I have to upgrade a
bit.

The complicating factor is that the glider is tied down on the flight
line in the summer, far from the trailer. Whatever I come up with has
to be a self-contained, compact and secure solution which will either
fit in the glider or is weatherproof and resistant to wind. Most 20 W
panels make excellent weathervanes, and the only securing mechanism I
have is the tie down cable and eyes. Since I live an hour from the
airport I need a "set it and forget it" solution that charges while
I'm away. I don't often fly on back to back days, and I do get some
recharge from the alternator on launch as well, so I probably need to
make up only about 6-8 Ah.

You've given me an interesting idea. I wonder if I could construct a
small aux battery box with a LN5014 DC/DC converter which I leave in
the glider to top off the battery after I leave. On return to the
airport I could remove the unit and charge it on the AC charger in the
hangar while I'm flying. If that few hours of recharge cycle time were
not enough it would be easy just to buy a second battery and swap them
out so that a fully charged one is always ready when I leave the
airport.

So this leads to two more questions....

Is the LN5014 ok to leave attached for that long (ie., is it like a
charge controller which will shut the current off when the main
battery is recharged)? If so, is it possible to do what you do with
respect to connecting my existing 300 mA solar panel and Morningstar
controller in parallel?