Having worked in the Automotive field for the last 14yrs, I can honestly say I've not seen tires last longer than 35k miles, if that. So 50-60k is crazy numbers to me.
Can you please provide the tire brand, model and size? All the information is on the sidewall.
We replaced the front two tires on my 2004 sentra @ 65k miles and the rears at 75k miles (whatever tires came on a stock Sentra in 2004)
Many newer all seasons are rated for 50-60k miles.
OP - For such a long trip, "all terrain tires" will actually make the drive more sketchy, noisey, and less fun.
Tires for mud, dirt, snow, etc usually have less traction on the road, and make a LOT of road noise compares to normal all seasons etc.
I would make sure you have tires that have more than 50% tread at the start of your trip, anything else is overkill.