We buy ours from a local commercial door company, Our typical standard is a Curries 707 door, ($250 for a commercial door with a steel frame is not bad, especially if it is galvanized.) Most come primed steel unless galvanized is specified. The galvanizing comes in several flavors, with the most typical being Cold Galvanizing G60 or G90 with the G90 being the heavier coating of the two. Top of the line would be a hot dipped galvanized door. The doors come in polystyrene core (R-6) or polyurethane core (R-10).
The frames typically come in two types, Knockdown and welded. Both types wrap around the rough opening, and are ordered to fit the thickness of the wall (finish to finish) Most frames can be ordered in 1/8" increments from about 2" to 13". The knockdown type goes in in three pieces and requires a smaller rough opening, while the welded type is designed to go in in one piece into a larger rough opening and then have the finish materials slipped in from the sides. With a prebuilt truck box the knock down would be much easier as it can be installed over a finished wall. There are lots of different clips and accessories available for installing the frames and making them more secure.
For those with deep pockets they make some cool frames with thermal breaks to prevent cold from transmitting through the frame. A couple of links below on the curries knock down frames (There are lots of other companies that make the same type of doors and frames, this is just the brand we use at my work. and again I would get a flush top cap for the door, and install a drip cap over the frame.
http://www.curries.com/Other/Curries...20Brochure.pdf
http://www.curries.com/Other/Curries...ech%20Data.pdf
you should have no problem getting the door bored with one or two holes, and make sure when you get a commercial door you specify the swing correctly, assuming its going on the curb side and you want the hinges facing the front of the coach, you would want a RHR (right hand reverse) swing which signifies an outswing door.
As far as door knob vs deadbolt, how about this option, get the door bored for both knob and deadbolt, and use a low profile door knob. These knobs are designed for when there is not enough space to install a screen or storm door with out it hitting a standard door knob. They only stick out 1-1/4" from the door, not much more than a deadbolt. I do not know of any that have a lock, so the dead bolt would be needed for the security end of things. Looked on up on line so you can see what I am thinking.
The Hardware Hut - Product #BAI-SALEM-LOW-PROFILE - Brass Accents Salem Low Profile Door Leverset
If you are buying local from a door company, bring along a sketch of how your wall will be built up, and they can help with the frame options to find the best method of attachments.
If buying online you will probably have less options for door frame thickness as most places seem to only carry standard wall thicknesses. The also do not seem to offer door galvanizing as an option.
Dave