Most of the cheap 12 volt inflators will overheat trying to bring RV tires up to spec air pressure. There are a few expensive 12 volt compressors designed for off-road racers, etc. I have a 2 gallon 110 vac Campell Hausefeld compressor
that can top off 75-80psi rear duals but it takes patience, technique, and a good air chuck that seals properly and doesn't let air escape. I have run mine using generator power on the road to top off tires. Shop carefully. There are a lot of small capacity compressors intended for 32 psi car tires, useless for RV's.