: I am planning to build a replica of the Chukchi kayak and would
: like to use raw leather as a framing material. Does anyone have
: advice on treatment and working methods?

If you are looking to build a replica with a real skin covering, the most difficult part will be finding a source for the fresh skins. How far are you from a zoo or marine-animal park that has seals, walruses, or sea lions in their collection?

These animals eventually die and the bodies have to be removed. Talk to the curator of the zoo and find out if they dispose of the dead animals themselves or if they deal with a separate company. Get the name of the guy who actually handles the dead carcases and tell him you want three to five hides when they are available. You'll also want the creature's brains if you plan to try preserving the hides.

Leather is tanned or preserved animal skin. If the skin is not tanned then it is a 'raw' hide, or rawhide. Usually rawhide has been stretched on a frame and dried in the sun. The hair may be scraped off or left on--depending on the use. To create leather, basically the hide is soaked in a mixture of chemicals that slowly soak in and prevent the skin from decomposing. Natives in the arctic didn't have a convenient supply of oak trees for the tannins, nor did they have the modern chemicals we now use. The only methods they had for preserving these skins were to pickle them in brine, smoke them, tan them with animal brains, or keep them cold.
There are articles on home tanning hides if you want to try it. Or you can skin the boat with rawhide and keep it extremely dry. Or frozen. It will be very smelly if it is exposed to any moisture. And it will attract bugs and mice. If you don't want to tan the hides yourself find a taxidermist and get their help.
Be prepared to pay a lot of money for these skins, and hopefully you'll find some lucky deals.

While you are waiting for the seal or walrus skins you should build the frame. While real sinew is available I think you can get an authentic look with synthetic sinew. Once you have the frame consider skinning that with clear vinyl so it can be paddled or displayed while you wait for skins. Having the frame on hand gives you a lot of credibility when you talk to people about obtaining uncommon animal hides. Local museum curators who see a good replica frame might be able to help ou make contact with skin suppliers.

I googled Chukchi Kayak and found that the Chukchi people also herded or hunted reindeer. It is possible that they used reindeer hides for some of their boats. It might be easier to find hides from other, local, common deers.
I don't think you want to use hides from cattle. The skin is much thicker and would be much more difficult to sew or even to tightly wrap around the frame. While you can get cattle hides which have been 'split' to make them thinner they still look like shoe leather, not seal or reindeer skin. I'm not sure if pigskin would be suitable, but that should be available from any slaughterhouse. Might want to dye that to get an authentic appearance.

If you go with tanned hides (leather) make sure the tanning process does not leave behind toxic materials. Hides cured for taxidermy frequently incorporate potent pesticides to keep them from being eaten by bugs. Last taxidermy demonstration I saw the taxidermist said she used liberal quantities of arsenic worked into the wet skins. That might be fine for a stuffed trophy in a museum but I wouldn't want it around my house, or would I want to sit in it and get small quantities on my skin.
Good luck with your project. It sounds fascinating. Send us some pictures as it progresses.
PGJ