Gaffers tape is flammable. Bad idea about a fixture. Beyond that, the glue when baked on tends leave a nasty residue. Not sure what sisalation is but a high temperature aluminum heat vent tape or Gam Tak tape would be a better choice. Otherwise 3M #23 fiberglass electrical tape works well in tapping stuff to hot surfaces without leaving a residue in removing them. I often will use it to tape the top - unsupported edge of a gobo to the frame holder so it doesn't get hung up upon removal.
Just one of your proud dealers doing his job.
Let's be fair to the other Gobo MFR's and Gobo dealears out there... One's job in offering advice - even tongue and cheek, also ends once one signs onto this website.Just one of your proud dealers doing his job.