I been going back and forth about taking my rear seats out my crew cab
silverado.The idea that i have if i remove the seats completely, is to
build a enclosure/amp rack that rear passengers can still sit on and
still be comfortable. I was thinking about covering both in some type foam and vinyl...have this been done before and would it work?

IMHO, if it can be properly designed, built and executed then I can't imagine any reason why it wouldn't work.  It's like anything else that requires such attention to detail, there's plenty of room to fail but if you can pull it off it will be great.

 

That being said, you'd really have to make sure it was carefully planned out and pay attention to the slightest details to ensure it comes out good without being a waste of time and money.  I can imagine several ways it could be done to come out great involving the use of aftermarket bucket race type seats or fiberglassing them in.  Either way it will be a hell of an undertaking, though I'm looking forward to seeing it done since I've had similar ideas for a couple of people here.

what if you just made like a normal rectangle box  with a nice thick foam and wrapped it so its comfortable? like a bench seat... idk i guess that would be my thought. just gotta make sure its secured really well incase of an accident. but that goes without saying.