It depends on the mods. The ones originally created by Crown will appear in a new store category, I believe US Farm Trucks. Some of them will appear in the misc category. The TLX ones, for example, will be there. The trucks though will be in the truck category. The RMC made ones will have a new store category as well, RMC mods.
The Holmer pack will be in auger wagons, and slurry I believe. The bulk pack will be in trailers.