I am not familiar with towmaster.
E 10 ply rating is a lot of tire. Sidewall inflation number will be 75-80 psi. I assume they are radial construction and not bias. You can check an inflation for load chart on Goodyear or Michelin websites so you don't have to inflate to sidewall pressure.
Your trailer should have the 6800# chassis, same as my 29' 1987 sovereign
A load range D tire by RMA (rubber mfg Assoc) is suppose to carry 2540 lbs at 65psi. Four tires would be 10,160 lbs. I figure I load out at 7000-7300lbs minus 810 hitch weight on the truck or about 6300-6500 lbs on the trailer tires. I figure I have plenty of reserve load capacity with LR D's.