Quality aftermarket high-alloy axle shafts
New wheel bearings and ball joints, also quality stuff
Aftermarket high strength wheel studs
^those 3 things will pretty much double the strength and durability of any high mileage OEM axle, but they cost 2X to 3X more than stock parts. So as you're wheeling it toward the failure point, have your sources and prices all lined up. And get the right replacement parts. Then you won't be one of these guys who's replacing it the 5th time.
Having said that, I'd still be slowing putting together an 8.8 in the corner of the garage. You probably won't need it for a year or two, so there's plenty of time to shop for excellent deals on the rebuilding parts. Because even though the 8.8 is strong, the factory bearing quality is around 150k miles, so it's gonna need rebuilt too.