Chances are that your powder can has a pretty good seal on it, and it has been sitting in your warm house before hunting season, too. Taking it from the car into the warm( humid) cabin is no different than taking it back home. If moisture was not clumping up the powder in the can at home, its not likely to have that problem in your cabin, either.
Because some cabins are very small, all the water used for cooking, and bathing( what's that?) can raise the relative humidity of a cabin pretty high. Cram 4-8 men in that small space, and their bodies add to the humidity, too.
If you worry about moisture affecting the powder, put the can in a plastic bag with a couple dessicant packs to draw any moisture that might enter the bag. You can buy those packs at most hardware( some drug stores), or hobby stores. They are easily restored by warming them in your oven to remove any moisture they have collected.
If you are hunting along a coast, or inland swamp or next to any large body of water, or river, you probably need to be concerned about moisture and your powder and guns. Clean and oil the guns nightly. Its part of the deal! If its pouring rain down for several days, no matter how " Dry " the country normally is, be concerned about moisture in your powder, and on your guns.
One last aside about unloading guns during a hunt. Seven members of my local BP club hunted deer on the same farm property one year. One deer was shot within an hour of the first morning. It was humid, foggy, and even misty most of the day. The manager of the farm had asked us all to empty our guns into a small tree that had to be cut down, due to damage done to it by deer. It was up close to the storage shed on the property, where he established " camp ". As hunters gave up their stands, and came in, we could hear them firing their guns back at camp, and the rest of us took that as a signal to start coming on in. I was the furthest away from the camp, and the last to arrive.
5 men where hunting with Percussion rifles, and NONE of the guns would fire the first time they snapped a cap! I had to get my nipple wrench out of my range box, and some 4F powder and help one of the guys take his nipple out, and put some dry powder under his nipple to get his gun to go off. He had failed to clean the oil out of the flashchannel before loading the gun that morning. 2 of us were shooting flintlocks, and both of our guns fired the first time we dropped the hammers. The 5 other guys practically went NUTS! But, within the next 2 years they had all acquired their first Flintlocks.
Now, the point of all this. While we were talking about the failure to fire issues, the largest buck any of us was to see, along with a fork horn walked( not ran) across a grassy area not 50 yards from where we were standing, and had fired off all those guns. Not one of us had a loaded gun, and only one man was actually standing with his gun, but his powder horn and gear were already in the trunk of his car! NO ONE got a shot at the deer.
You might think that 7 shots fired in the same small area would spook the deer away from that spot from a quarter mile around, but instead, the deer came right through the lawn area of this hobby farm, and ignored the presense of an open fire, and the talking, laughter, and shouts of all those humans.
This is one reason I think most people put too much concern about firing a gun off back at camp. I don't think it bothers deer at all. For some, they will be curious as to who the new neighbors are, and will come around to check you out. Deer in farm country are used to loud noises associated with humans, be it from cars, tractors, combines, Railroad engines, banging doors, or sounds and smells from houses, and businesses. Farm country is actually pretty noisy these days. Deer in Farm country are also used to human odors, fire, smoke, the sounds of chain saws, of falling trees, and dozens of other sounds associated with working farms, and the building of homes and barns.
Now, I am open to the suggestion that in true Wilderness country, deer and other game may react differently to smells, and sounds. I just have my doubts. I was out West one time where I thought I was in true wilderness- in the mountains with no one else to be seen as far as I could look in any direction-- until a jet plane flew over, and disturbed the quiet with its engine noise. If you look at a map of all the air routes now used by commercial air traffic, and then add in the routes used by private air planes, Its very hard to find any place in the Lower 48 states where their might be " Undisturbed " wilderness left.
I still fire off my load every night when I finish hunting, so I can clean the gun thoroughly and know for sure that the gun will fire the next day. When my gun was new, I did pull a couple of the balls with my nifty, new, ball puller jag, but that is a lot of work.
Friends convinced me that firing a shot off near camp created no more problem that all the banging of car doors, the camp house door, the outhouse door, and all the noise made by us in the cabin.
Our problem with seeing deer was that they were bedding down in grassy areas on the two properties adjoining the one where we had permission to hunt, and were simply passing through this property going from one to the other. The deer could care less that we were there.
Without permission to hunt the bedding properties, and with no one hunting there after opening day, we had no way to get the bucks out of their beds and move across the property where we could hunt.
When I hunt anything, I take the time to NOT slam the car door, or to make unnecessary noise. I also don't cough, spit, clear my throat, or eat out of plastic bags, unless they are kept in a large pocket that muffles the sound of their " crinkling". I do listen to the squirrels, and birds around me for alarm calls that telegraph my presence to the game I am hunting. I unlock my knees so that I glide down forest trails to my stands, rather than stomp down to them with the walking gait I use in town. I do want to get into the home area of the game without them knowing that I have arrived, much less where I am at.
Good Hunting.
