Well, I did it the way I did due to having most of that stuff on hand
I did try a gasket. It was neoprene foam rubber (kids placemat) but it ended up being open cell foam (although very tiny cells). I was going to order 1/32" Neoprene rubber (not foam) but never got around to it. Also, if I put in a gasket, it leaves a space between the fins and top of the inside, which wouldn't be ideal.
I can always build a new top. I'll just have to find out who sells Lexan around here. Home Depot only has 1/8"
I used to "lap" (sand
) many various pieces of metal at a previous employer. It was an 8" wide belt sander and they modified it & put a metal bar across the sand paper, and one down each side. You could literally just place something on the moving sandpaper & it would just sit there, getting sanded away.
But, at home, all I have in that category is a Dewalt 1/4 sheet random orbital palm sander. I tried it, I'd be there for HOURS.
This block still seems salvageable for now, until I pay off some bills & get more $$ on hand. If I didn't have the bills, I would already have a CNC mill