: What size to purchase for a Night Heron???

For most home built kayaks it's best to make a tracing of the cockpit and get a custom skirt/cover made. The upcharge is usually very minimal and then you know it'll fit. I get mine from Seals and I think the difference in cost is like $5 or $10, not much.

You'll need to mark the position of the seat too, as some sit further forward or aft depending on how the cockpit was outfitted and for whom it was built, some are shorter/taller.

Bill H.