It's hard to not make it look like crap. For what it's worth, I have had some success with the mindset of "this will never look factory". What I mean by that is, most people try to get as close to factory carpet as possible and it still ends up looking off. I scrapped that idea and wrapped several of my previous enclosures in black vinyl and they turned out pretty good looking. This is the only pic I have on-hand.
Use cardboard templates to get the cuts just right if you're doing a custom fit. Fiberglass is not that hard if you watch some good tutorials, so consider that option as well.
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