I traded a '70 Yamaha R5 for a '64 short-box Econoline and it was a major hit w/the ladies. So my friend Hank decided he had to get in on some of that.
I had a nice, deep feather mattress in the back. You could fluff it up and two people could be in the middle and not see over the top.
Hank decided to one-up me so he got a water bed into the back of his van (an ugly blue long box, year unknown). I told him that thing gonna weigh a TON, but he was unswayed- it was gonna have a water bed and that was that.
Later, after the wreck, I saw what a ton of water would do to the front seat mounts of a van! He had slammed on his brakes for whatever reason, and the WB became a freaking TIDAL WAVE that crunched him into the windshield, breaking the rear seat mounts right off the seat/floor and pinned him there until he was able to get himself out.
He survived w/nothing more than a badly bruised body- and ego. Fortunately, no one was w/him at the time.