Toys (boat) and Class C

Have you considered a truck camper? A boat is the reason I have a TC. I can haul the camper while towing the boat. I can set up camp by taking the camper off the truck. Then, I have the truck free to launch the boat or go sightseeing or whatever.
I've saved money on parking at zoos and amusement parks by leaving the camper at the campground and just driving the truck. It's cheaper to park a truck than an RV apparently.

Texas, Oklahoma, Missouri on Corps of Engineers lakes, someone tows the boat with the truck that will launch it, and the RV gets towed out or motored out separately. In some cases, the park might be so close that the same truck makes two trips, towing out the RV and then the boat. Not unusual for 3-4 vehicles plus RV at each campsite, in the Corps parks here.

This also works at the Oklahoma and Missouri state parks, which tend not to have entry fees and are often as roomy as the Corps parks. Texas parks complicate things a bit more with daily entry fees, which probably influences choices in Michigan and Indiana parks.

It may depend somewhat where you intend to go camping/boating. If you're staying in Michigan, you can double tow a boat behind a fifth wheel (within certain restrictions and having the appropriate license endorsement), but there are a number of states where double towing is not permitted or has onerous requirements (primarily along the east and west coasts) and having a fifth wheel would require bringing a second vehicle to tow the boat trailer...or making two trips instead of one.

If you have a class C, the options are indeed to unhook the utilities to launch, or to bring another vehicle, or to find a friendly fellow camper who's willing to do it in exchange for some beer or whatever.