I'm ready for final welding on a set of full rear quarters on my 71. I have a plan of attack for everywhere but the drip rail area. Not much metal there and mine is VERY thin. My spot welder won't reach and i'm almost afraid to try to plug weld it. Hopefully someone has some pics of how they welded theirs, or some advice. Here's a pic of the area i'm talking about, and a few of how the project is coming along. And yes of course i'm gonna clean up that area before i proceed. Thanks in advance !!

I punched 3 small holes in the small flange area of the quarter that meets the drip rail. I plug welded and used a cutoff wheel to carefully smooth off the plug welds.

I've drilled 1/8-3/16" holes in the flange area like Ed suggests and plug welded them without too much trouble, the weld will generally fill the hole quickly and still penetrate without burning through.
What you might also consider is to do the opposite and drill into the drip rail flange and weld to the quarter panel flange if it's thin.

Panel Bond

Steve O.