More fodder;
your thinking correct on speed rating and long term reliability for tires on a trailer in those conditions.
Check out he Goodyear Wrangler HT in a LT215/75-15 D load range at 2096 lb capacity/65 psi with a Q speed rating.
Goodyear make over a dozen Wrangler tires so make sure its the HT type tread
Or a LT235/75-15 C load range at 1985 lbs capacity/50 psi with a Q speed rating...this tire is made by several usa tire manufacturers so it should be available just about anywhere.
Yokohama RY215 700R 15 load D. This is a euro size and made for vans/suvs and trailers.
Goodyear Cargo G26 225/70R 15 C 65 psi...another euro class tire made for trailers/vans/etc
I towed for a living in NM/CO/TX/OK/KS/LA/AR/MO so I understand heat from high ambient temps/road surface temps and high heat generated by different tread types.
I found a low rolling resistance tire tread like a highway tread (HT) or especially a ribbed tire tread like the Bridgestone R-250 run the coolest making a 12-14 hour run at interstate speeds in those high temps carrying max loads.
A AT type tread can generate more heat at interstate speeds.
