DougW, I believe you are mistaken. NavyLCDR is correct. 20 watts is just a trickle charger. You could probably leave it hooked up in storage to keep your batteries charged, but charge controllers are so inexpensive it seems silly not to have one installed. Connected in series would be pos. to neg. You are pos. to pos. which is parallel, and correct. If you are very careful with power, you can probably go a few days without damaging your batteries. Get a Volt Ohm Meter (very inexpensive) so you can check your battery voltage. If you get below 12.1 volts you are damaging your batteries. Definitely hook up the solar. Every bit helps.
2009 Roo 21ss + 2007 Superduty 6.0