mdm, that's great. Perhaps once you get a result you're pleased with you could post a scan and start a new thread that doesn't say "= Failure"; though I guess anybody really interested would probably get past that title and read on. At any rate, awesome.
If I recall the UltraStable instructions correctly, the melinex in CMB's Tod Gangler video is plain, uncoated. That is what allows it to act so well as a temporary support. If that's the case, people sure are wasting a lot of effort in making "temporary supports" when just plan melinex will do.
update: Yeah, the only prepraration for the plastic sheet is:
The plastic sheet (typically 5-7mil clear polyester) should be washed
thoroughly with powdered soap (Comet) and a soft sponge before
use. This will give a slight “tooth” to the plastic which will help
pigment film adhesion. Cut the plastic sheet at least one inch larger
all-around than the final paper size.