I haven't finished reading my book on 12v electrical systems yet and this thought just popped into my head, so I thought I'd just float it out there rather than actually think about it myself (which will undoubtedly produce better results than my thinnking!)
So- is it possible to wire up your TD for 12v and then not wire it directly to a battery, but instead wire it directly to the charger/ converter. I want to be able to add a battery (small or large) at some point for camping off the grid, but in the meantime be able to run it off the electrical hookup at the state parks.