Actually, you need federal authority if you are doing interstate transport. If you are only intrastate, you need to meet the requirements for operating authority in your state.
Are you pulling only for one dealer? If so, you don't need authority; you can operate as a private carrier. However, if you are "for hire" you can apply for authority on the federal web site. Once you apply, they will send you some paperwork that you will need to complete including insurance/bond info etc. It is kind of a pain.
I got lucky and leased to a single dealership for RVs and am able to operate as a private carrier. We got our DOT number online in only a few minutes.