If you are looking at that large a unit you might also check out NRC Modifications. Their factory is located about 5 minutes east of Haulmark and Renegade. You see a lot of 40 ft plus units from NRC around the drag strips.

I have been through all of the factories except Dynamax and I found Haulmark the least willing to make any changes. Renegade makes a lot of different models but also somewhat limits what they can custom build. Showhauler, United Specialities and NRC are more willing to custom build a floor plan or features you want.