Good looking paper trailers are available from Team Track Models for $6 download. You can buy the blank trailer and decorate as you wish. Downloadable Paper Model Kits for Scale Railroad Buildings (teamtrackmodels.com)
A free old style tractor and 40' round nose trailer are available on DAF.com. They're about S scale, so simply print them at 150%. I scrubbed the lettering with grey "marker" in the pdf file before printing in this case.