When is it good to Sand/ Media blast your car?
I would just wire wheel and por 15.
Think about this for a minuate, you are wanting to sandblast a rust free car.
Where is some of the sand going to end up, trapped in your 1/4 panels, rockers etc.
Most people who blast have to replace sections in the 1/4 panels, rockers etc, so these panels are removed and the excess sand will come out.
I think in your case you would actually be contributing to rust if you blasted in your case.