My air compressor is a 12VDC model and I sit it on the tail gate of my truck. I use the Q Industries portable MV50 12VDC 150 PSI Air Compressor to use with the CAMCO 36153 Blow Out Adaptor for blowing out the water lines... Since this unit is tankless it takes time to slowy build up air pressure which makes it very safe to use for blowing out plastic water lines. Both units were ordered from AMAZON - It has a long hose and will reach all the trailer tires, the truck tires, and will for blow-out of the water lines all from the tail gate of the truck.
My 12VDC cable fits just fine plugging into one of my trailer batteries sitting on the trailer tongue area. I'm not sure how much 12VDC it needs to operate but the clip on battery connectors are pretty large. I suspect your 12VDC plugs would have to have large cable feeding them. Being directly connected to the battery is probably a better thing to do.
Sample photos from google images