i saw a pic on the internet the other day of the "redneck hot tub" and a guy put a tarp over the bed and filled it with water.
i couldnt resist trying this my self.
i did all the math and it was 2679lbs of water in the bed. around 330 gallons.
i put the jack under the reciever to take some of the weight
and then me enjoying my new hot tub