I would use the navy for sashing, but I would make the sashing pretty thin, since the logs in the cabin aren't very wide ( I mean, from what I can tell in a pic), but that's just me. Someone else might have better ideas than I, I'm kind of a noob.
If you want, take a big piece of the navy fabric, and lay out all your blocks on top of it spaced out the same distance you want your sashing strips, and then take a pic. Review, rearrange, take another pic, plus you can see how you like them all put together without the sashing.
ETA: LOL, looks like Ethel and I had the same idea at the same time!