I wouldn't blame him. It would certainly be good to purchase him at least something warm, in case they don't sell raincoats. Goldenrod, from my knowledge, has the widest selection. Your best bet would be to shop there.

Ah, I aim to waterproof my bags. While sleeping, I can simply keep them within a tent, but during travel I'm not exactly able to do such a thing. Lining them with tarp would hopefully do well in keeping the water from ruining anything, such as my journals. I would hate to lose those.