Atlanta is not all that bad as long as you don't try going through during rush hour. We usually hit there about 10:00 am. There is always traffic, but it moves.
You can use the HOV lane with the boat as long as there are 2 or more of you in the MH. We take it all the time and have passed or been passed by the popo and never been stopped. There are always landscapers and contractors using it as well with pick-up and trailers with 2 or 3 people in their truck. You just need to watch the signs since there are some left hand exits from the HOV.
The advantage of going through downtown all the semis have to go around unless they are making an in town delivery so they are few and far between.