In Europe, MB has a nifty tow hook, which is one piece and hitches to the rear suspension. Your local MB dealers will tell you that MB-USA does not recommend towing vehicles. But when I lived in Europe, I saw all kinds of MB towing things like boats, camping trailers, etc. It sounds as if your SeaDoo is rather light, and there should be no strain on your car.
However, you will have a heck of a time finding a company that will install a towing bar on your car. I would caution using ones that drill holes in your uni-body; your car in not a frame-body configuiration, but rather a unit-body in which the body is the frame as well. And you will surely invite rust where they have breached the galvanization on the body by drilling.
So check in Canada; they can get things that we can't, duer to MB-USA's fear of litigation. Canada is really a good source for things Benz, and they are just across the border!.....Andras