Here is a magazine blurb from the 1960s, which describes the above photo long before before the term "trailerable trawler" had been invented:
I'd be a bit concerned about weigh aloft myself, and just how do you get the car on and off, anyway? This one makes more sense:
Terra-Marina disappeared from the marketplace a long time ago, but the idea was revived a few years ago by a German company. Sealander came along and reintroduced the notion of a combination camper-watercraft, usually shown powered by a Torgueedo electric outboard.
Depending on options the price ranges from $17,500 to $19,500.
There's lots of romantic photography establishing the brand:
There's only one problem that I can see.
Where does one go to the toilet, if there's no place for a toilet? The swim platform is dual-purpose, you say. So much for romance!
But wait...Here's the answer from the same magazine review:
The Benches convert from generous seating (up to 6 adults) and dining to a spacious bed. The Sealander Caravan has storage below the seats and can even be customized to include a toilet, a cooler, a sound system or even a barbecue. Other features include a stainless steel wash and cooking module with cover plate, a single flame gas cooker, a tap with water pump, a 10-litre-fresh-water tank and a 10-litre-waste water tank, as well as a gas case and a fire extinguisher. With a closed sunroof, the Sealander is now your safe haven from wind and weather. Be it out on the water, or on dry land.