Oil, or leftover water or coffee, urine or whatever in the flash channel or breech will do more to spoil your hunt than any moisture "drawn from the air" will do. Cleaning a rifle by fire light, or poor light in general in camp is a good way to do a less than perfect job also.
I NEVER clean my BP firearms with water, and never have...so I think you would be fine cleaning the gun like any other in camp if you had to, without the rubber-ducky treatment. Yes, BP rifles and shotguns can be cleaned just like "regular" rifles and shotguns. Water cleaning is NOT required or "best", it's just how many/most prefer to do it. I've been cleaning mine like "regular" rifles and shotguns for around 30 years...NO PROBLEMS.
But again, if your rifle is TOTALLY free of moisture and oil when you put in your hunting load, and you keep the nipple capped, and change caps often, your load will stay good. When the gun is uncapped overnight (legally a BP firearm is technically UNLOADED when uncapped or unprimed...unless things are REALLY different in Texas)keep a piece of leather or something between the nipple and hammer to seal it.
What is easy to do at night is to just remove the nipple, make sure it is clean and clear and dry, and look into the flash channel and double check that. Some guns you can see, pick and poke right into the main charge and check it too.
By the way, BP fouling does not in it's self attack the steel, it attracts moisture, which then will rust the steel.
But again, it cannot be stressed enough, the gun, breech, nipple, and flash channel must be TOTALLY oil, solvent, and water free when you initially load it with your hunting load. If so, it will fire normally YEARS after being loaded, let alone a three or four day, or longer hunting trip.
Good luck.
Rat