Caulk, sealer, or undercoating? Need info please

[Stangsx2]

Working on my '69 Mach 1.
I've primed my frame and am ready to re-apply seam sealer, caulk, and or the black rubberized undercoating.
I have some seam sealer in a tube, and I have some automotive strip caulking.
But I'm not sure what was on the body to start with (see photo). It looks like there was a bit of undercoating material that I scraped off, but it seemed to be in odd and random places. And I can't really tell where the seam sealer was or if there even was any. Also, if I used some automotive strip caulking, is that a type of seam sealer, and is that stuff paintable?
Can I use the seam sealer where ever there are seams, even if there was none there originally?
This all sounds rather rambling and random. I just can't seem to find adequate information about the seam sealing/caulking in my restoration books or on the net.
Thanks for any and all feedback and help.
Brian.

 

[chromedog]

ok... the stuff ford used was junk, it was fine for a few years, then dried out and crumbled. strip caulk is not going to harden, so if you are sealing anything you want to be really watertight, dont use it. the best thing to use, imho, is either a two part epoxy based product, such as sem, or fusor.the best idea is to seal anywhere there are two pieces of metal overlapping each other.

 

[66 Restomod]

In the cowl area and the side boxes behind the fenders there's far more seam sealer than that area actually needs, particularly with today's high-quality seam sealers. That old seam sealer looks like it was applied with a big brush and they just wanted complete coverage to last as long as possible (and wanted to do it really quickly). We are in the process of seam sealing my stripped car now, and we are just going along ALL the seams with a small brush rather than making a big mess.

 

[chromedog]

i personally dont like a brush at all, but if you use the stuff in a can, you have no choice, unless you put it in a heavy plastic bag that youve cut one corner out of. also, to get a really neat job, run a strip of masking tape on each side of the seam, as wide as you want the seam sealer to be. run your sealer, then smooth it down with your wet finger. you can then remove the tape, and astound everyone with the neatest seam ever!