There is no real GMRS base station.

When radio users refer to the "base station" it is a GMRS radio you would use in your vehicle powered by a  DC 50 amp power supply. If you have multiple radios you can use the same power supply to power them, although you would NEVER want to key both radios at the same time as bad things can happen. For an antenna you will want to use as roof mount antenna or if you have a metal roof you can use a mag mount antenna. There are many different options you can choose from.