If the Fort's carts dont have a cig lighter socket, the easiest solution might be to bring your own 12-volt battery to power the inverter. Sure, it's more to fit into the cart, and more weight and bulk to haul in your rig, but it sure simplifies things! If you are in a motorhome, you could use your/one of your coach batteries for this purpose... you aren't using it when plugged in at the fort. You probably don't want to use a chassis battery, or a tow vehicle battery, which would erase radio station programming and reset clocks, etc. If you are using a coach battery, you can just reinstall it during the day to recharge it. If you bring a separate battery, you may need to bring a small charger too.