Personally I'd check the GVWR and see if you really need that third axle.
I have a triple axle toyhauler with a GVWR of 18,000 lbs. If I was fully loaded I would have around 14,400 lbs. on three axles, or about 7,200 lbs. on double axles. If I were running 7,000 lb. axles with Sailun tires, which are rated at 4,000 lbs. then I would be covered for 8,000 lb. per axle.
However, I run about 3,000 lbs. under my GVWR when fully loaded. I could easily run double axles and would prefer it. If nothing else the maintenance costs are much greater with the triple axle. Consider 6 tires, 6 sets of brakes/bearings, extra expense if you do any suspension modifications. Thanks but no thanks.