Yes this can definatly be done.I would suggest you contact a local car audio place and they should be able to fix you up.Companies like Audiovox ,etc do offer fax machines for vehicles.Its quite a simple install,and the machines are quite small and efficient.
Good luck!
One thing though you will find that for a fax transmission the vehicle will have to be stopped and parked or else there will be too much noise and therefore errors.