Welding & Repair Process for Bodywork?

[Panici]

I'll be patching some rusty spots on my E30 this year, and it's my first time attempting body work.

Based on some research, here is my plan. Please let me know if there is anything I can change or improve.

1. Protect/Cover any nearby surfaces (from grinding, welding, overspray, etc)
2. Cut out rusty metal (until clean metal is reached).
3. Sand or wire wheel the edges to be welded until bare metal.
4. If repairing panel where you can't get to the back afterwards (rockers), clean/degrease and then spray on weld-through primer on the inside. [Will this stop rust from forming?]
5. Make template on cardboard, transfer to sheetmetal.
6. Cut and bend sheetmetal to fit.
7. Clean/degrease surfaces.
8. Spray weld-through primer on back of patch piece.
9. Butt weld with tacks, alternating sides and allowing time for metal to cool.
10. Grind tack welds flat.
11. Clean/degrease surfaces.
12. Coat with POR15. Allow to cure.
13. Sand POR15 smooth. Clean/degrease.
14. Spray Colormatched paint.
15. Spray 2K clear.
16. (For panels with no backside access) Drill small access holes in hidden areas. Spray something like Eastwood Internal Frame Coating.

I'm looking for a repair that has the best chance of preventing future rust. Ideally i'd like the repair to be invisible unless inspected up-close.

I'll be using a Lincoln Easy MIG 180, with gas.

[roguetoaster]

Seems like you're all set, but I can add that I prefer to sand or wire wheel the edges to be welded as it keeps them at original thickness and reduces the chance of burn through.

Also if welding near glass you need to cover the glass to prevent pitting, same for nearby painted surfaces although they're less likely to be damaged.

[TobyB]

[Will this stop rust from forming?]

nope. A wax like 3m rust fighter or waxoyl will, though...

And I try to butt weld as little as I can. It's so much more likely
to shrink than lapping does. Often, you have to, tho, so tack, grind,
do bodywork to shape the panel then weld more, repeat...

t