In most states, the gun is legal to carry or transport if the cap is removed from the nipple. Don't take a loaded gun indoors if the outdoor temperature or humidity is higher or lower than the indoor temperature. Leave the gun in the truck or on a porch out of the rain. As long as it is dry, the powder should be able to stand being in the barrel a couple of days. Same with the lube. As long as it does not heat up, it should not melt or run.
Before re-capping, always check the nipple with a wire, or ' nipple pick ", to make sure the flash channel is clear and dry. If thee is moisture in the flashchannel you will get a tiny bead of moisture on the wire when you take it back out. Use good light to inspect the wire. If its dry, you are ready to go. If moisture is even possibly a problem, get some of the pencil erasers that you put over the top of a worn out eraser, and keep them in your kit. You can put one of them over the nipple and lower the hammer to hold it on, and that will keep moisture out of the nipple, flashchannel, and main charge. Or, get one of those stick erasures, rectangular in cross section and about 3/16 by 3/4 by 2 inches long, and simply use the hammer face to clamp that rubber eraser on top of the nipple to seal the nipple from moisture. The main spring will be heavy enough to keep that erasure firmly on the nipple, and no moisture will get in. If you can find a cheaper, and thinner scrap of rubber- wish we still had rubber innertubes- use it instead.