Okay, I'm doing it this way:
Took measurements from the inside of the boat, then took ¼" off dimensions to account for foam planking and made a crude form:
The green part is the piece I made for a foot rest earlier, which is now the after end of the forward buoyancy tank. It's held to the form with screws, so I can remove it.
First plank goes on:
It's hot-glued to the aft bulkhead and to the end of the plank on the other side. The planks aren't attached to the forms at all.
Three planks on now:
The little spots you see on the seams between the planks are where I stabbed the seam with the hot glue gun, melting a space into which I injected hot glue. This is so the edges align with one another. This was pretty time-consuming, as I had to hold the pieces together until the glue hardened; about 5 minutes for each spot. But it seems to work.