It sounds like the "plant components" might be quite heavy so "Rollen" might actually be "rollers" in this case. For "Transportwagen" probably need a term that sounds heavier-duty than "trolley", so your idea of "transport vehicle" would be fine because it would be quite universal, or "truck", "carriage", "lowboy truck/trailer", "dolly", "low bed truck/trailer", etc

Terms from Ernst – "Wörterbuch der industriellen Technik"

"Transportation/movement of the plant components is (to be) carried out on rollers or on a transport vehicle, etc., etc., etc."

HTH - Dan