I'll just toss in my 2 cents here.
You don't need to repack your bearings every time you go through water. You could to be safe, but in reality it's not that common for the grease to be fouled. Running water, like a river is more likely to foul the grease, and going too fast through standing water increases your risk. Anyway, I put about 25,000 miles of driving and offroading on my truck before I repacked the bearings and the grease was still good (doesn't mean this applies to everyone, just don't think you have to do it with every puddle you go through).
Like the other guys said, there are better places to spend your money that manual hubs. Get some good 31" tires and go wheeling with a local Xterra club. Find out what kind of offroading you like and see what mods others have that do the same kind of driving you do. Then go from there.