Thanks for all the info, I guess the highly compressable insulation would be there for any misalignment of the plug which should probably be flush with/or below the surface of the roofline, I also understand that sometype of metallic tape was used to cover over the screw holes on the plug,
so just to double check the install, I will stretch the vinyl top over the plug, glue inside the window channel and install the 3/8" stainless keeper, does that sound right

thanks again
john