My tube bumpers have seating for two in the rear, and two in the front with optional arm rest,

I park my Jeep with a couple of friends and I usually just sit on the dirt, but my friends sit on the bumpers... all they do is just put a coat or something under it and they don't do that half the time...

But that hammock thingy is cool...

 

I saw something similar to what you mentioned.

It used one of these types of carriers:


There was a pad on the top of the carrier to make a seat, then It had another insert into the extended part of the hitch (under the carrier) that had a little table on it. so you sat on the seat facing rearward, with a small table in front of you, i think it was just a two seater though.

Hope that made sense.

 

Now that'd be a riot on the freeway...