We stayed at the hotel on the exhibition site so we could walk to the show undercover all the time , we went by ferry from Hull to Rotterdam and drove over to Dortmund all worked out OK for our needs ,once the car is parked we left it there the three days ,as everyone says it takes this to do it justice . I do not know if anyone else has done this but if you walk over the foot bridge in front of the entrance going in to town ,on the left a few hundred meters yo will come to a resturent that is a Mongolian barbecue all you can eat for one price and it's very good . What helped me was Google Earth for the hotel location it shows up as a Best Western but now it's a Mercu hotel
It all worked for me but everyone is different ,maby cheeper accommodation is available but it is not as convenient .
David