Got new 4.80/4.00-8 tires/wheels. They are load range B, 594 lbs at 60 psi. I doubt I'm loading 1,200 lbs in the trailer. Should I run them at 60 psi or something less?

 

60 is max, way too much, unless you are near max load. 32 should be fine.

 

I run 25psi in the 8" tires on my Harbor Freight Tag A Long trailer. Too much pressure and the trailer will want to bounce more on bumps.

 

The 60 pound marked on the sidewalls is NOT the recommended TP for use.
Just the max that the tire should be inflated to.
Same reasoning on the MC sidewalls.

The tire manufacturers have no idea of how the tire will be used.
All depends on use and load.

My Road Dog trailer has a label stating what TP to use and it isn't 60 lbs.