Your guns are not going to instantly turn to rust when using black powder. 50 to 60 rounds of 3 dram loads and a wipe of the exterior before putting into the case and you are good to go. I take with me a dish pan, dish soap, use hot water and a snug fitting jag and patches. A good bore brush and a few minutes cleaning until the patches come out clean, dry and oil. I use Slip 2000. You can leave the cleaning until the next day without any harm. The fouling is a bit harder but still cleans easily with the hot water and soap. A English type 12 bore chamber brush works well or a US 10 ga. bore brush with a bit of 4-0 steel wool wrapped around also works well. Soap and hot water quickly dissolve the powder fouling and the brushing loosens any hard deposits. I've been doing this for 45 years and have never had any problem with rust. The plastic dish pan makes the hotel staff much happier that using the bath tub and one can sit outside and enjoy a good cigar while cleaning the tubes.
