If you're not going to shoot above 95 degrees, around here you wont be shooting in the summer at all. Bore Butter and Crisco both turn into very thin liquids in a matter of seconds.
I use #11 CCI caps on my Hawken. I don't seal them with anything. I don't plug or seal the muzzle but I do keep it pointed down. I really don't see water getting past a tight, lubed patch but I just don't take the chance.