Gotta agree with Jordan, I think by far the easiest solution is to buy a converter/charger. This will effectively "bridge" your 110VAC and 12VDC systems so that you can run all the 12V
lights/fans off shore power when you want to, or off the battery(ies) when not connected to shore power. It will also charge your batteries when connected to shore power.
Edit: (Heh, just read through Rick's post and realized I'm giving the answer that he already knows and doesn't want to see again-- sorry, my friend!