Depending on where you live, it might make sense to just send him with some money to buy his warm clothes in ID. We live in CA and one of my brothers served in Des Moines, one in Minneapolis and one in Denver. I think all three of them ended up buying winter coats in the field because we live in a particularly warm area in CA and just can't get the kind of clothing locally that you need for winters like that. Plus, less stuff for them to lug through the MTC. Check out missionarymall.com (I think). If I recall correctly, they'll guarantee suits for 2 yrs and they'll also ship things directly to them once they're in the field.
Wife to a great DH, SAHM to 3 great kids