The base doesn't have to be fancy. Before I made the steel base, I used a 2x4 piece of wood with a 1/2" hole drill all the way through for the primer to drop.
NOTE* Since my 1/8" blue steel punch sits only two inches above the top of the case, I use a pair of pliers to hold the punch so my fingers will not get whacked or pinched against the brass. And it usually takes two or three taps of a lightweight household hammer to remove the primer.