Weld Through Primer usage?

Stumbling into some metal fab on my car.  There's a section of the frame rail that I will be cutting out and replacing with some new metal.  Do I spray the inside and outside with weld through primer?  Inside to protect against corrosion since it isn't water tight in there.

Thanks.

I like to spray the inside, or anything that won't be accessible after welding, weld, then spray the outside with more primer or paint after it's cooled.

If going weld through primer, spend the bucks on the copper colored stuff. Eastwood et al, are not very good (opinion, toned down to avoid saying they suck). 

I'm leaning towards just painting with cheap paint, and cleaning off where it welds, ala Fitzee. YRMV

Weld through primer has minimal burn back so it's good to have it in the Heat Affected Zone (HAZ).  Everywhere else it's best to have normal primer and paint.  It's alse expensive you you don't really want to waste it where it's not needed.

APEowner said:

Weld through primer has minimal burn back so it's good to have it in the Heat Affected Zone (HAZ).  Everywhere else it's best to have normal primer and paint.  It's alse expensive you you don't really want to waste it where it's not needed.

That suggests that cheap weld through primer isn't very good.  Which makes sense- I've had problems welding to weld through primer.  Need to get the expensive copper stuff, apparently.

alfadriver said:

APEowner said:

Weld through primer has minimal burn back so it's good to have it in the Heat Affected Zone (HAZ).  Everywhere else it's best to have normal primer and paint.  It's alse expensive you you don't really want to waste it where it's not needed.

That suggests that cheap weld through primer isn't very good.  Which makes sense- I've had problems welding to weld through primer.  Need to get the expensive copper stuff, apparently.

The expensive copper stuff is better to weld to but it's still not the greatest corrosion protectant and it's even more expensive so my preference is still to only use it in the HAZ. 

Time will tell how it holds up but I've taken to using brush on Rust-Oleum inside things like torque boxes and unibody "frame" parts.  It offers good corrosion protection, doesn't require primer, it's relatively inexpensive and since it's applied with a brush, prep and cleanup is minimal.  I use cheap disposable brushes.

I really liked picklex.   It works well and seems to protect the metal after a few years.

Do the OEMs use weldable primer? If so, I would find out what it is and use that.