Three good sources for building skin-on-frame kayaks are:

1) The Aleutian Kayak by Wolfgang Brink 2) Wood and Canvas Kayak Building by George Putz 3) Baidarka by George Dyson

Brink describes how to build a single baidarka, but his descriptions are general enough that they could be applied to a double.

Putz presents plans for a 17 ft. single with a small cockpit and a 18.5 ft. open cockpit boat.

Both Brink and Putz use canvas over wood construction.

Dyson's book is a little different, going into the history of baidarakas and his history of building aluminum framed baidarkas covered with nylon fabric. His book contains plans for a double, but the building detail is for aluminum tubing. It could undoubtably be adapted to wood consrtuction. Dyson's book is worth owing for anyone who has ever though about kayaks and their history.