Here's another rollbar for the Traxxas TRX-4 Sport. Best to print with Ninjatek Armadillo or some type of Nylon but ABS or PETG should work fairly well too. I'd avoid PLA unless you plan on taking it easy on the rig.
Best to print it laying flat, like the bed is the truck window, legs up in the air. You'll need some supports unless your bridging is insanely good. Suggest at least 2 exterior walls and 40% infill or higher. Layer height won't matter too much.
Purchase gets you the Rollbar model and an installation template model to help align screw holes.