I applied the Spectrum to the painted metal of the cab. We cleaned it, taped it, sprayed it. I haven't found a need to scuff anything if it's SUPER clean or new. The stuff sticks like crazy.
I believe(key word) that I read where you can topcoat the Spectrum but you have to wait for it to dry. Specifically it was pertaining to bedliner over the Spectrum....but I would imagine that would go for paint too. Something like 30 days of dry time. It's water based...so I think the stuff needs to fully cure and get all the water out of it.
I'm torn on the spraying of the Spectrum....it takes a long time to build it up. I think my brain is programmed that somehow this stuff should just come out at 2-3mm thick in one coat. It takes a LOT of coats to build it up. This was probably 1mm thick but again, there's probably 3mm on the inside of the truck on this section.