I got my old rear deck filler panel off by drilling/grinding/hacking/cussing the spot welds out from the top side. There are some I accidentally went all the way through at the lower portion by the trunk gutter. I was going to repair the holes and drill out holes in the new panel to plug weld it in. A friend mentioned I should just go ahead and drill out the remainder of the metal in the gutter portion and plug weld them upside down from the trunk to the new panel. Any thoughts on this?

Also, I'm worried that water will get in the gap between the gutter and new panel and start rusting. There was no seam sealer in this area should I use it? What about weld thru primer?

Thanks.

I would plug weld the panel from the topside everywhere you can.
But on the spots you ALREADY drilled throu just drill out those spots with a 1/4 bit. Just weld them up from the bottom. This a procedure done everyday in body shops. You are doing nothing but welding it from the bottom instead of the top, it affects nothing!

Clamp the panel in place and make sure its tight before you start welding.
The use of weld thru is simple. You apply it on the two mating surfaces that will get welded. The weld thru provides some type of corrosion protection to the weld site.
Once the panel is welded in remove any weld thru that might have gotten on the panel, like overspray.
Weld thru has NO adhesion properties, its one and only purpose is to provide some type of protection to the mating surfaces that will recieve the welding.

Do I have to remove the paint in the gutter and the black EDP coating on the new panel before applying weld thru? Also, should I use a seam sealer in the gutter area when finished? Thanksf for the help.

Any thoughts on this? I really need some advice thanks.

Do I have to remove the paint in the gutter and the black EDP coating on the new panel before applying weld thru? Also, should I use a seam sealer in the gutter area when finished? Thanksf for the help.
Yesterday 10:55 PM

Dont remove the black coating or ecoat!
Only remove the paint on gutter where it meets the new panel. Grind it to bare metal then spray your weld thru over the bare metal.

As for a seam sealer I only recommend a 2part seam sealer. 2parts wont crack and shrink up like a 1K seam sealer tends to do.
I like Duramix products, Id use a product called control flow for that seam. Controlled flow will flow out very nicely and not leave a high ridge mark on the edges.
To get a nice seam take some masking tape and run it just past the seam about 1/16 on each side. Apply your seam sealer, allow it to cure for about 3 mins and pull back the tape. You will have a nice sharp line, and the sealer will flow out a tad so you wont have that high edge mark.

But make sure you apply some type of primer to any bare metal, other then weld thru, before you apply any type of seam sealer. Id use epoxy or even urethane primer will work...Eric

Thanks for the help Eric, I appreciate it.