As Frank said, you can just cut out the warp and glue in a new piece, it just looks like 1/4 inch balsa. Your over thinking it. You can glue it on straight using pins, once glued down and set up is should be fine. The little warp in the rudder can be removed with your covering, you bend it straight and use your heat gun on the other side of the warp and the covering will tighten up and hold it straight. I just use ammonia and water {the windex trick} it's the ammonia that softens up the wood. You can try spraying the inside of the warp to remove it.
Or the EASY WAY. Just buy some 1/4 inch balsa and cut new parts if you mess up the warp. Sometimes you can make it worse!
Kit builders should have 1/4, 1/16, 1/32 and 1/8 sheeting on hand in there shop for these little problems. Not a lot but a sheet or two. Hobby People have balsa in stock and Hobby Town but they charge a bunch for it. As a scratch builder I buy it in bulk from National Balsa and it is very cheap that way but you need to buy too much. Kit building friends are always hitting me up for a piece of wood so if you have any builder friends make a phone call, we don't mind helping out.
