Most infant carriers are designed to be strapped in using existing seatbelts... pretty much any seat that has seat belts should be able to hold it securely.
Is there a third seat in the Freightliner that has seatbelts? That should be fine. If the "toter home" has seat belts for a dinette or something similar, those should work.
Fire departments and Police departments are used to "normal" cars when showing how to install infant seats - they may look at your rig with a blank expression, lol! They could very well help you, but you may want to contact the seat maker or Freightliner.