Lots of good info here. And there are pages of discussion on 2m antenna mounts on this site, so I won't repeat that info.
Here's what I'll add:
2m mobile is a pretty light lift, and as others have pointed out it's great for vehicle to vehicle coverage, and when you have repeaters in the area it's handy for regional communications, too. But Alaska is big. So I'd expect lots of areas with not so many people, and with no close repeaters. But 2m mobile is a very handy thing to have, in my opinion.
HF mobile is a big lift, to do it right, in my opinion. I wouldn't jump into that until you know what you might want. With the possible exception of 6m and 10m, you can't just stick a small antenna on top and expect it to work well. And most of the time, 6m and 10m aren't going to get you any better distance than 2. (I'm making generalizations here.)
BUT... A portable HF rig is easy to do these days. If you want to learn, and have some fun, take along an HF radio, and the stuff to setup a simple wire (dipole) antenna. Wherever you park or camp, as long as you have some room you can setup an antenna and talk around the world. 80m and maybe 40 would cover most to all of Alaska, probably farther on 40, and 20m would give you options for longer distances. And you don't have to mount anything to the truck to do it. I would plan and test this at home, in the backyard, first.
Agree with the others on getting your general. It's multiple choice, there's no code, it's pretty easy and gives you way, way more options.