I see this topic discussed quite often with no real answer. With just buying a 32,000 GVW truck, and no CDL, I wasn't sure of the answer either. I wanted to post what I found just for future reference of anyone else looking to buy a truck over 26,000 pounds in the future. Of course laws vary by state, so be sure to contact you local state police first to be sure, but this is what I found for Michigan:
The only commerce that can be done without a CDL is if you are a farm and traveling within 150 miles WITHOUT hazardous material.
As long as you are not using the truck to exchange any sort of money, tax write off or even trade of goods, you do NOT need a CDL. Upon calling my state police the guy was asking questions of what I planned to do with it, what I was hauling, who I was hauling for. As long as you can answer that it's only for private use then you are not required the CDL. It doesn't matter if it's a 18 wheeler or an RV, if it's only for personal use, then you don't need your CDL. I am putting a 'Not for hire' on the side of my truck just for a little more insurance from the cops.
Even with this the cops themselves do not always know the laws. I will be putting the phone number of the Michigan State Police transportation department in the truck and the print out from the Michigan.gov website where it states no CDL is needed for private (no commerce) use. This way if they try to hold me too it, I will have something to fall back on.
Be sure to call your local Secretary of State (mine didn't know) and/or state police to be sure that these same rules apply where you live.