1995 Buick Roadmaster Wagon as a Dinghy?

Far as transmission goes contact REMCO TOWING DOT COM. It'll fall in one of three categories. Towable as is. Towable with one of their lube pumps. Or no way. You could use a driveshaft disconnect, but first be sure you can get a baseplate for the critter.

"Also quite a few states have towing restrictions once weight is over a certain minimum for brakes on the towed vehicle."

Once again, it must be stated that such laws refer to "trailers", and the legal definition of "trailer" in many states does not include a towed motor vehicle.
Do NOT trust any list of towing laws found on the internet. I have yet to see one that isn't inaccurate in many ways. Sometimes the inaccuracies are minor, such as stating that Montana has a speed limit for towing vehicles (there is no such law) or that the legal length for a truck/trailer/trailer combination is 65 feet (No, it is 75 feet). Sometimes the inaccuracy is a little more major, such as stating that Montana has no braking requirement for towed motor vehicles (actually, there is such a requirement. It is called a Braking Performance Law, and it applies to all vehicles and combinations of vehicles. See MCA 61-9-312)

You need to check the towing capacity of the Class C. I think towing the Roadmaster will be like dragging a Battleship Anchor.

I would find something more suitable as a toad. JMO

Also quite a few states have towing restrictions once weight is over a certain minimum for brakes on the towed vehicle. this can be checked on the internet, as I have found a state by state chart before. Some go as low a 2,000#.
FOUND THIS
Buick Roadmaster Estate Wagon, model year 1995, version for North America U.S.
4-door wagon body type
reference weights: base curb weight: 4563 lbs

Base on this information I would say not to try to tow it.:(

Base curb weight is over 4500lbs.

My first thought is "NO!" It is quite likely transmission damage will result due to lack of lubrication of the output shaft bearings and seals.
However, it is possible that a driveshaft disconnect can be installed, which would allow towing.
OR, you could just get underneath and remove the driveshaft from the differential yoke, wrap tape around the u-joint caps to hold them in place, and tie the driveshaft to the underbody securely. Be sure to put the u-joint fasteners in a safe place so the driveshaft can be reinstalled.
The Owners Manual, if you have it or can get it, might have towing instructions.
Keep in mind that Buicks are not exactly lightweight vehicles. It wouold be a good idea to weigh the car. It is likely that a Class C is limited to 3500 lbs or less towed load.
Good luck.