I would pick one set of tires that work well with whatever gearing you have, probably some light mud terrains as they will work well all around. Pulling a trailor with a 4 banger across the counrty is not something I would like to do.
I have done the to big of swampers on the weekend and small all terrains for DD thing and these things always wheel better all around with a good set of all around tires that go with your gearing anyway. If I were in your shoes that's what I would do.
Other than that, a good tune up, grease everything well and change your fluids all around. The spare rear driveshaft was god advice too... Take a wireing repair kit, a spare thermostat and some spare u-joints. It's always the stupid little stuff that bites you on a road trip.
Have a fun trip, sounds awesome. You had better post some pics up here as you go.