I would think it would say on the can what u could thin it with, or what it suggest for clean up.
Lacquer thinner would work also but thin to 10% first and see how that is before u thin it out too much.
If you don't care a whole bunch on how it looks, you could just skip the primer and shoot a good acrylic enamel on it.
This is often done with farm machinery and it works well for the long haul.
One of the reasons primers are used is to create a uniform color below the surface of the top coat so no color variations show up in the top coat,but I don't get concerned about that on a trailer or farm piece
A good acrylic enamel can be had for 30 to 50 bucks a gal. and two good coats could have your truck looking like new.
It's all about what u want in the end and the bucks you want to spend really.
Dan
