DerbyDad03 wrote:
I'm going to be replacing my windows soon. I plan to use minimal
expanding foam to fill the gaps.

The Great Stuff for windows (blue can, "Will not bow frames") says
uncured foam can be removed with acetone. Can I assume that the
acetone will not harm the vinyl?

I wouldn't. Instead, I'd suggest the DAP latex-based expanding foam.
It cleans up with water.

If you insist on using the sticky Great Stuff (wear gloves), remove the
extra after it's dry. The limited-expansion stuff sets soft and you can
just tear it off with your fingers or cut it with a utility knife.

Do I need to put foam in a 1/8" (or smaller) gap?

Absolutely. It might work to tape a smaller tube to the main tube,
something small enough to fit in the gap.

--
Warren Block * Rapid City, South Dakota * USA