The obvious culprit to your rust problem is probably corrosive ammo. The fact that you are not sure if you used corrosive ammo or not is why I'd assume you did. You mention rusty bores ONLY on your 30-06 (maybe corrosive ammo) and your Mosin Nagants (surely corrosive if it was surplus). Classic corroded bore.
Other guns only had minor surface rust. Corrosive ammo requires more than just normal cleaning. Maybe you didn't clean the corrosive salts propey? Maybe you used a rag cantaminated with corrosive salts to also clean or wipe your other guns? Sounds like a reasonable explination to me...
Storing guns near a steamy shower area is not a good idea for obvious reasons. Move your cabinet. Buy quality oils and cleaning gear.
