I'm just waiting on an adaptor hose so I can hopefully hook my gas bottle up to my welder and I'm ready to have a go at welding the rear valance on so hopefully it's dry tomorrow.
What I want to do is wire brush all the surface rust off the panel and spray "weld through primer" on it before tacking the rear valance in. I've not had much luck with trying to do spot welds or plug welds when I've tried to weld before so I was just gonna run a few welds along the lip and weld up the outside of the closing panel. Or should I drill a few holes and try plug welding it?

To be fair I'm fairly happy with the fit, lines up quite nicely with the closing pannels and the 3 mounting holes for the bumpers are about right.
Not done much to it over the last few dsys, replaced the rear brake lines and used stainless steel brake unions. Replaced the shoes and springs just because they're cheap to replace and a few electrical things like riveting some earth points in the engine bay.