I tried to install my wheel to the Barstow with Multidae method but I couldn't get it to show up in the parts selector. Then I put the files to the Barstow's folder in the content folder and it worked. Can somebody tell me what's wrong with the .jbeam? (I suppose that's where the problem is after looking at other wheel mods) I installed the dae and the front wheels' jbeam inside a folder in mods>vehicles.
It should be inside mods\vehicles\barstow. You can make folders in there too, like mods\vehicles\barstow\wheels or something if you want.