the thing you need to realize is that color coat is a flexible coating. here is some information from SEM's website
https://www.semproducts.com/product/color-coattm-aerosols
HANDLING AND APPLICATION
PREPARATION:
VINYL:
1. Clean first with SEM Soap and a gray scuff pad.
2. Rinse with water or wipe soap residue with a clean damp cloth and allow to dry.
3. Clean thoroughly with Vinyl Prep or XXX Universal Surface Cleaner using a clean, damp lint free towel and
wiping in one direction.
4. If contamination still exists, water will bead on the surface. Repeat this step until beading no longer occurs.
PLASTIC:
1. Clean first with SEM Soap and a gray scuff pad.
2. Rinse with water or wipe soap residue with a clean damp cloth and allow to dry.
3. Clean with Plastic & Leather Prep or XXX Universal Surface Cleaner. If contamination still exists, water will
bead on the surface. Repeat this step until beading no longer occurs.
4. To promote adhesion on ABS, PVC and other similar plastics, apply a medium wet coat of Sand Free. Color
Coat should be applied while Sand Free Adhesion Promoter is still wet. As the Sand Free Adhesion
Promoter evaporates, the Color Coat is drawn into the surface creating excellent adhesion.
OR
To promote adhesion on TPO, EPDM, PP and other similar thermoplastics, use Plastic Adhesion Promoter or
XXX Adhesion Promoter.
the second part of your question - why not replace the elephant skin in the trunk? first, is that the new product does not match the original that well. to do the entire trunk you will need at least 3m of elephant skin. and then you either have to remove a gazillion staples and re staple all of the elephant skin on the trunk floor boards ... then you get to the rear trunk panel, the pieces that are adhered to the inside of the fenders ... then the 2 panels on either side of the tool box on the trunk lid. in my opinion, if your panels are not ripped or have damage to them, i would clean them and maybe repaint them.