Depends on OEM wheel/tire size.
I keep P rated (44-51 psi) on all my single axle and lite weight tandem axle trailers under 6k lbs.
Whats great about a P tire is it is available anywhere and will travel at any highway speeds.
Tires on a single axle trailer don't have any side scrub issues like a multi axle trailer so no need for those heavy stiff sidewalls in a C or D tire.
"good judgment comes from experience, and a lot of that comes from bad judgment" ............ Will Rogers
'03 2500 QC Dodge/Cummins HO 3.73 6 speed manual Jacobs Westach
'97 Park Avanue 28' 5er 11200 two slides