Greg, I'm retired from the Md Prison system. For more than ten years there, my duties included firearms instruction. I was picked to be an instructor because I was about the best shot around, and knew oneheckuva lot more than most everybody else about firearms in general and shotguns in particular. I taught hundreds of Correctional Officers to shot, including many unmotivated, inexperienced,stupid or getting their input on weapons from action movies, or all of the above.During that period,I was also on the weapons squad of the regional tac unit,and wrote some of the techniques,procedures,and regs for the Division concerning firearms and their use.
Before that, there was a war on,and I got a little piece of the farm. Have a shoulder that lets me know when it'll rain and some pretty ribbons.
I regard a shotgun in TRAINED hands as one of the best self defense tools possible, for the massive amounts of energy that one can dump into a target. I do not regard a folder as a good choice, from long experience.
As for a travel gun, I'd go with a 30-30 Winchester or even a lever action in a pistol caliber. Shots may run longer than the 25 yards or so where the shotgun shines, and stray pellets are more likely than stray bullets.
Also, this has come up a few times before. I suggest doing a search, and note that few serious WIHTF types either use or advocate the use of folders.
Finally, it's your life on the line, use what you think is best. All I can do is tell you what I've found to work, and why....