If you watch your battery load you don't need a generator unless you desire air conditioning. An overnight stay suggests coffee made with the gas stove,prudent use of lighting, and any 12VDC accessories. Add up the amperage draw of each light, your DC TV, and compare against the rated amperage of your batteries. You shouldn't draw them down more than 60% before recharging.
BTW, overnighting at WalMart or any other free parking lot is not boondocking, or dry camping. It is overnighting, whether it be WalMart, Flying J, Love's.
2000 Winnebago Ultimate Freedom USQ40JD
, ISC 8.3 Cummins 350, Spartan MM Chassis. USA 1SG, retired;PPA,Good Sam Life member."We the people are the rightful masters of both the Congress and the Courts - not to overthrow the Constitution but to overthrow men who pervert theConstitution. "Abraham Lincoln"