good weld-thru somewhat permanent primer?

[Ochre]

Curious about this as it pertains to some rust repair I'm embarking upon...

as far as I can tell, the factory didn't bother to, or did a piss poor job of finishing the backside of the door striker panel, and the area between the back bed floor and rear cross sill. This is why I theorize that there's always, if not almost always, surface rust in these areas, and the back sill area rots out (besides the fact that the rear hatch area leaks badly, and the "sandwich" of metal traps water and causes rust in that area). I have a few thoughts with regards to semipermanent fixes in these areas:

It seems to me that these areas are particularily nasty to deal with in a few respects:
1) both the striker panel/bedside and back floor/rear sill sandwich metal to metal, trapping dust & moisture that happens to get in there
2) both these areas need arc & spot/plug welds to join panels
2a) heat from welding damages most automotive finishes (apply before)
2b) por-15/rustbullet/etc aren't billed as weld-thru
2c) because the metal "sandwiches" together, applying finish after welding is difficult/impossible
3) weld-thru primers are just that, primers. Most primers will rust thru given a long enough timespan, and/or a difficult set of environmental conditions (high humidity/salt like here in MN)

Given those constraints, a few thoughts spring to mind, pre-paint:
A) Use a non-heat method of joining panels (glue) - makes me nervous
B) weld unfinished panels together, find a method of spraying an anti-rust finish (like thinned por15) into the unfinished panel and sandwich
C) spray anti-rust compound into area in vicinity of weld, weld plug weld and hope heat cures compound properly - also makes me nervous as even the coldest process for welding (mig) is still way higher temps than any rust compound I've seen takes to accelerated dry
D) seam-seal edges of sandwich post-welding - could trap moisture, or let moisture in thru a pinhole over time (also messy and looks like ass upon close inspection)
E) perhaps my best idea so far, finish panel but grind spots to be plug-welded and spray weld-thru primer on those areas (good assuming no interaction between the different finishes, and that the rust doesn't get under the anti-rust compound

I'm curious what other members have to say about this...I'm looking at investing tens, probably hundreds of hours into repairing the rust on my blazer, which I intend to keep for some time. The last thing I want to worry about is...drumroll...fixing more rust! I'd rather worry about fun things...like more horsepower and more gears and which rims look the best, etc.

It seems to me that these are key areas, along with the rocker boxes, that seem to rust out to some extend on every blazer/jimmy, regardless of location due to inherent design flaw. Mostly, it seems to me that little or no thought was given to where water would flow, settle and escape (or not)

Naturally, the thing to do would be to correct these design flaws, with some corrective surgery - but most would prefer to keep the stock looks as well as the inherent difficulty of corrective actions (most require extreme welding, done incorrectly this warps panels, putting us at a worse position than simply square one). Plus, if done incorrectly (and only time will tell) the additional weldment will make panels that need to be repaired a second time harder to remove and fix.

So, I'm curious as to some member input on good weld-thru primers that can withstand the test of time, to keep my ride rust free for as long as possible after my current battle with rust. Is that too tall of an order?