As long as you stay under length per state you are in you're are ok. As you know it ranges from 65' and up and each state can be different on that. However, after that the laws are the same as far as being an RV or NOT commercial. Keep the trailer clean, no decals or big wraps.
You still need to make sure you are not overloaded on any axle, gross or on the tow vehicle. I know in Ga, Fl, and SC you can only get tags for so much weight as a non commercial vehicle no matter what you do.
A 28' is not a big stacker so you should have no problem with of getting a tag weighted correctly for the tow truck.