Shasta 16SC or Airflyte Goucho Dimensions

So I finally purchased my foam and am trying to decide on a gaucho cushion design.  I've come up with 3 options.

Note : Large pink dots denotes where cushions would be attached to each other.
          Dark lines would indicate where I would use vinyl ( using another fabric on the other side to make it more         comfortable to sleep on, thinking vinyl might be hot)


Gaucho designs by Corvett crzy, on Flickr

If you have a chance please take a look and share any opinions or thoughts.

1.  Only connection is at the top of the two back cushions.

2.  Thinking that the back would stay in place better, plus have a larger area without seam for the hubs.

3.  Typical design with all connected, however it would result in having to make the whole thing vinyl or sleeping 
      half on vinyl.

Thanks!

To remedy that I thought about making one side of the back 16" long so it would extend down behind the base cushion, the other side would still be the 10".  I thought this would keep the back in place and make a wider sleeping surface (without a seam directly down the middle) when in bed mode.  My total overall width in bed mode is 48", base width is 29" max. was going to go 28".

I've never seen this configuration so I wonder if there is a problem I'm not seeing.

I am going to try something a little tricky. I have my rear bed base cabinet pulled out at the moment. I realized that there is no reason I can not bring the front of that lower cabinet out into the room a bit further. This will give me a deeper sofa seat during the day. I also have the style of trailer where the but/back sticks out. (See my profile picture). This was not formerly used as part of the sofa and was dead space. I plan to allow the rear piece of foam on the gaucho to sit into the dead space and then the front cushion will actually be taller and hide it. This will all take a lot of math and configuring, but my overall goal is a deep seat sofa for during the day and a wide as possible bed at night. I have not decided yet if I will sew together the couch pieces. As an upholster I have made them before, but with the configuration I am creating it may be easier to leave the pieces separate. I will post photo's when I get to the point sometime later this year.

You can see in this photo on the staining of the wall, that the cushions and seat did not go back very far originally. The newly framed area will all be part of the gaucho now. This redesign will I hope be a big improvement. 

ladywendolyn What do you think is the best tool to cut foam, leaving the nicest edge finish?
I've used a serrated knife, but I also saw someone had used a sawzal. Opinions?

I would use a very long razor edge knife. My wife has a Creative Memories knife with a blade that extends to nearly 2" so you can cut through the entire thickness at one time. I now use this to cut foam insulation as well. Previously, I had used a serrated edge of a sawzall blade and it created a huge mess. You know the foam fragments that stick to everything, and are like magnets on your clothes due to the static energy?! The razor knife cuts through the stuff like butter with a clean edge and no mess.

I can't make mine work! It's a newer one my mom had, good condition. Wonder what I'm doing wrong??