: Is this a misprint? Did you really put a 1/4" wide gasket in a
: 3/4" wide slot? How's that work?

There's a mis-statement, but not that one. I used a 3/4" wide x 1/8" thick - or "tall" - strip for molding, but then chamfered the edges to more or less 45 degrees to make layup easy; that left a channel 1/2" at the bottom since you lose 1/8" on each side to the 45 degree chamfers. To correct the mis-statement, I used 3/8" wide x 1/4" thick weatherstrip for the actual gasket.

The finished hatch sill, as seen in photo, goes something like this: From wooden edge of hatch opening there's 1/8" flat lip sticking out, then the 3/4" wide gasket channel, then another 1/8" flat to finish it off and provide protection for the weatherstrip. The total width is therefore 1 1/8". It's kinda yellow colored because I used Kevlar in the layup.

Don't ask me why I used Kevlar, I just did. No regrets, though. Looks kind of cool, I think. :-)