Trailer tires

Gang,

I'm leaving this Friday to pick up a glider that I purchased 1100
miles away. The trailer looks brand new, but is about 12 years old,
as are its tires. The glider and trailer weigh in the vicinity of 950
#. The tire spec from the owner is :
Carlisle Sure Trail ST
ST205/75014 (replaces F78-14ST)
Max Load 1760 lbs @ 50 PSI (actual load will be under 500 lbs)

I plan to buy 2 new tires before the trip, and stop at the first
service station after the pickup and have them mounted. Question is,
what to buy. It does not appear that the trailer has any suspension,
so I think I'd run the tires slightly soft, maybe 25-30 psi. I was
wondering about whether it should be radial or bias ply? Any
particular brands?

Thanks in advance,
Ed