Well, I've camo'd all three of my current fullsizes.
First one was the crewcab. Took about 20 cans each of primer and paint (Rustoleum gray auto primer, Krylon ultraflat tan and black, Rustoleum flat brown.)
I washed it, sanded and did some body work, and primered on top of the existing paint.
Second one, my M1009, I went all out, used an air spray gun, the whole nine yards. I don't know that it's THAT much better. Washed, alcohol, sanded the body work, primered over the existing repaint. Had a local body shop custom make me the paints.
Last one is my wheeler. I think I washed it, mostly, or at least rubbed the crap off with a rag. Usually. I did grind off lots of Bondo and then welded in various rust holes. Primered with the Rustoleum gray auto primer, and the blues are three shades of Rustoleum semi-glossy "Painter's Choice" or somesuch.
The key to a good paint job is prep. IMHO you need not sand off the existing paint to bare metal *if* it's in good shape. If there is any flaking or peeling or whatever, though, it's gotta go. Washing is a must, and alcohol prep to get the dust off is prolly a good idea. I would rough up the surface for decent adhesion of the primer.
Also note that a camo paint job hides many sins; one, as you have different color zones, and two 'cuz people expect a bit of redneck quality *(or lack thereof

) with a camo job.
The Smurf camo on the third truck gets compliments even though it's pretty crappy.
I think the M1008/1009 patterns are in my gallery here; if not, PM me with yoru email addy and I'll send 'em to ya ... all of mine are done with those patterns and I think it adds a certain authenticity, or at least a certain insanity, to them.
Now, if you want a show quality job, go read anything Ryoken's written -- that guy's forgotten more than I'll ever know about bodywork -- but if you're gonna rattlecan it at home, I have some expertise there
-- A