Haha ... there's a good reason for that.
The cabin on a LC is about 4m long, about 1.4m wide and might be 1.2m high. That's around 6.7 cubic metres, which means that it would have to weigh over 6.7 tonnes to sit on the bottom of the water.
It's like a boat - a boat displaces a certain amount of water and you will see cargo ships measured in terms of tonnes of displacement - that is referring to how much water WOULD be in the space occupied by the boat. One cubic metre holds 1,000 litres of water and weighs (pure water) one tonne. Nice and simple (which is especially important for me coz I dunt like my brussel sprouts).
By comparison, the D40 Navara has a cabin 1.4m wide, about 1.6m long and 1m high. That's a displacement of 2.24 cubic metres = 2.24 tonnes. If the car weighs more, it sinks. If it weighs less, it floats.
Remember that the tub needs to be added to that equation.
Work out your potential displacement, and make sure that you weigh MORE than that, or you'll need to also fit an outboard motor!