Wow three years FT is impressive and must be fun!
I get an email when someone posts in this thread - and I also can't believe it's almost 5 years since my first question! Still have our 347. Stayed in it three months over the summer last year and not since - hopefully soon though.
For tires, you might consider a commercial truck tire like BFG Commercial T/A, Michelin XPS, or Firestone Transforce. We put the Firestones on ours in 2011. They've been to AK and back and a couple trips to FL - no probs and hardly show any wear.
The weight rating (3042#) on these don't mean much. ST tires have an easier rating system than passenger tires because they technically don't haul passengers, so a lesser factor of safety on them compared to commercial truck tires.
Good luck