I contemplated most of the above and decided on the following a few months back....

I purchased a like new RV [recreation vehicle] power supply/charger/120AC power panel with multiple AC and DC breakers, complete with enclosure. $60.00 at an RV bone-yard. This device provides the means to have a 30 amp AC power supply, 12 VDC regulated power supply with an automatic charging system, circuit breakers and power distribution buss for AC and DC. The unit is small and enclosed in an metal enclosure.

I utilized a 30 amp capable #10 gage contractor power-cord much like an RV would use but it's longer. I have a small ventilated compartment [accessible from the exterior and interior of the trailer] which house's two group 27 hi-capacity Sealed maintenance free 12 volt battery's, coupled to the power distribution buss, DC to AC power inverter and a regulated solar panel for battery maintenance when out and unhooked from the tow vehicle. When towing the truck or motor-home charges the batteries automatically as required, while at home the power converter handles all the work.

I additionally rigged a 16 VDC regulator to provide a power source for charging TX batteries and other things requiring more than 12 VDC input. This is somewhat redundant with the DC to AC inverter but you don't have to carry around the AC powered wall wart's and such. I have the batteries coupled in series and parallel to achieve either 12/24 VDC.

Is it overkill probably... But works flawlessly and is rather simple. Nearly every RV and Marine application produced, currently utilizes the same components. All is readily available at Marine and or RV parts suppliers.

For the simplistic approach as mentioned by others you can purchase at a RV or Marine parts store a raintite standard 2"x4" size electrical faceplate adapter which has a twist on or spring loaded door which will accept nearly any grounded #14 gage or better extension chord female end. It could'nt be any simpler, just obtain a chord long enough for your needs and your plug and play...