Hauling with Toyo Proxes or Nitto 420S

Hey guys! I have a quick question. Does anyone know of I can haul with Toyo Proxes or Nitto 420S tires? I saw in Diesel Power mag where a guy hauled his massive camper with them. I have to haul a 33' Sundowner gooseneck horse trailer and I'm hoping to get 305/45/22 size tires. Does anyone have any thoughts on this? Also, does anyone know of any great helper springs/or anything that I can keep my truck from sagging with? I'm not sure exactly how mug the trailer weighs but I would guess about 15,000 pounds since it has a steel frame. Any help would be appreciated! thanks guys

Check the load rang on the tires. If they are E rated you should be fine. As for springs you should try the firestone ride rites. They are great and won't change how the truck rides empty.

Does anyone know the load rating for either one of these tires in size 305/45/22?

I know my 305/50/20 proxes ST II's are 8 ply's rated at 3086lbs max load. I would think a similar size might be the same but not sure. I tow with mine just fine.