I think my first question would be why is one brake dragging? Here's a few things I'd check. This would require raising that side of the trailer and pulling the wheel.
Also, assumption is Dexter 4 piston calipers.
The pads are retained by a pin, pull the pin and check if the pads are stuck due to rust or wear on the caliper housing.
with the pads pulled you should be able to easily (relatively) inspect the piston dust boots. If the boots are torn then they can allow water in. The pistons are steel, caliper is cast iron add H2O and = rust. The rust can cause the pistons to not retract slightly, creating drag.
These calipers are repairable if you want to mess with one. The caliper carries the seal and the piston moves across it. The surface of the piston must be unpitted and minor surface rust can possibly be cleaned up. The caliper needs cleaned up too. Dexter sells caliper repair kits, seals and dust boots. After you do one, the next one is easy. When I did mine, the one thing I added was DOT 3 compatible grease on the piston OD, seal, caliper bore and a daub under the dust boot. Theory is that the grease's job is to fight corrosion and prevent sticking like you might be experiencing. Then the fun begins, bleeding them. Got tips for that too but depends on your rig's hose config.
I also carry a IR Temp gun after I had a nasty hot rotor from rust. But been smooth sailing and stopping since my fixes.
2005 Dodge Ram 2500 5.9L 6 Speed
16" Michelins, Hi Spec Wheels, Max Brake, Carslile Actuator, Equal-i-zer, Dill TPMS. Campfire cook.