Semantics aside it seems your asking about a double tow which is perfectly legal in MI as well as about 30 other states. As long as your hitch and truck are up to the task you can do it.
I'm not sure I'd try it with a pontoon however. From what I've heard those things are a chore to tow solo. The have a rather high center of gravity compared to other boat types. They catch a lot of side wind and a lot of drag.
I would want some kind of electrically controlled brakes on the boat trailer which is unusual. I would want a brake control in the cab set up separately for the trailer brakes so I could apply them to "straighten things out" if need be.
If your` just going 50 miles to a local lake it may work out. If you have in mind of towing it all over the place all the time I think you'll grow tired of it quickly.
A pointy, low, fiberglass hulled boat would probably tow a lot better.