I'm pretty close to replacing my door pillar panels.... what's left of them after rust. I was wondering if supporting the underside of the car is needed. Is there a special supporting I'll need to do? Thanks for whatever help you have.

YES! It's critical. The more support points, the better, and from front to rear. Eight or even ten supports points are not too much. The biggest problem you will have is getting the car absolutely level, just like it sits on the pavement. Make careful measurments of the whole car before you start (the distance from the LEVEL surface it sits on to all the areas on the car). Record them religously. Make sure all of your supports are the same height or at least deliver the same measurements plus the recorded measurements you have recorded for each part of the car. When you can get the same measurements, with the supports added in, of course, you should be ready to start working on the car.

Thanks Toby. I figure it's time for stocking up on 4X4's and shims. I know i can get iron shims in varying sizes and hopefully the larger sections of 4-8" square post from and old iron shop I have worked at. I'd much prefer the non giving iron to the wood. I'll try to do each side individually also.
Once again thanks.