What kind of mini-mobile are you driving? Guns don't take up
that much space and I'd certainly pack at least one extra shotgun in the event one of your guns fail (it happens
).
To answer your question as to which shotgun I'd choose if I were on the trip you've described, it'd probably be my 12 gauge Benelli Super Black Eagle II. Relatively light weight, very reliable, multiple chokes and a 3 1/2" chamber make it a very versatile shotgun indeed.