TIN sliding door rail

I took the sliding door off to take care
of rust behind center sliding rail. There
seems to be some kind of thin foam on
the back side of the rail, but it’s old
partially gone with the removal off the van.
I am thinking to get rid of the foam
remnants. Would you apply anything at
installation ?
I am thinking seam sealer around holes
for the bolts to keep moisture out of those
holes, anything else?

That’s most likely a VHL tape and it would be a good idea to replace it with something similar. It’s relatively self sealing if properly applied and should prevent the track from rattling against the body sheet metal.

I would get some 40 thousands thick VHB tape. You don't want the rail against the paint directly, it will wear through and cause rust again.

I also have 18mil helicopter tape (thickst available, I think - 0.46mm), but I guess the double-sided tape is better for this appilcation, correct?
I was thinking to put the helicopter tape in area where mudflaps touch the body and rub through the paint, what do you think?

You want something with a bit more thickness than 18mil. Double sided adhesive isn't required, but is suggested.

The advantage of double-sided tape is that it seals the grit out better than a single-sided tape does.
Grit under the arch trim could wear through a tape face as easily as paint?

-dave

Is it ok to put Butyl tape between the rail and the body?
It should do both jobs, sealing off the screws from water, and keep the rail from rubbing against the paint directly.

Tacking onto this since is still on the list and even the mighty POR could not stem the cancer. I need to get in behind and really clean this up. Is it just a waiting game for the release of the foam tape? That is one sticky mother of a tape. I tried some torch heat - nothing. I thought the divots in the rail might be spot welds. I gave up due to time and weather. I had removed the torx bolts from the rail bracket but with the minor release I got of the rail from the body, reattaching the bolts was a real chore.