I try to avoid using abrasive paper if possible, it's expensive and slow and sanding epoxy clogs the paper. It also produces poisonous dust.
I use a cabinet scraper to level epoxy coatings. Takes about 2 hours to level a kayak exterior. There's no dust, just epoxy shavings. A 6" wide scraper produces flat surfaces without any scratch marks.
My favorite scraper which I have used for 30 years of proffessional woodworking was 3" wide when I bought it and it's 2" now, so the cost is negligible. The edge doesn't last long used on epoxy and even less when glass is encountered so I have several and sharpen them together. I make them myself by cutting up worn out handsaw blades on a metal guillotine.
The page address is for an article on how to use and sharpen scapers. When I scrape epoxy I don't hone the scraper on a stone, I just file the edge square with a fine file.
I also use a scraper to level and smooth paint, primer and undercoat, and varnish.
The page address is for an article on how to use and sharpen scapers.