I made a post on the Hammock Forums outlining this project asking for input from folks with more wood-working, boating, and hammocking experience and got a lot of great feedback.

A lot of the input questioned the stability of the raft and whether it would actually fit on the roof of the Jetta.  I had only briefly considered these two components, though fitting on the roof was a critical design factor, I hadn't actually gone through with testing it.

So today I did.  I tested the stability of the raft by trying to tip it over while it was on the lawn and I lifted the frame up on to the roof of the Jetta.  Both tests were successful!
In this photo, I'm holding the frame at an angle while it rests on the roof rack rails.
Mounted and strapped in.  Come game time, I'll flip it so that the deck side is down and the barrels can be lashed in and carried on top.  Additional cargo will go in the back of the car or lashed to the up-turned frame as necessary.
Perched on the edge of the raft, I felt absolutely no tilt or wobble. I know that it will behave differently in water, but I don't have access to water just yet to test that fully, so this is the best I can do with what I've got.
Even leaning to the side, I wasn't able to get the frame to lift up and I'm 245lbs.

Next, the deck!
Here is the song that I heard on the radio that inspired me to build the raft.
The vertical hammock posts are built! They slide in to the slots at either end of the frame
I still need 2 more 6ft lengths of PVC so that both sides of the tarp can be up at the same time.
It was Little League Day at Safeco & Mark got to parade around the perimeter of the field. Along the way, we saw Brandon Maurer in the dugout, but Mark didn't want to get his photo taken as he was feeling a bit shy. Once we made it back around to the stands, he changed his mind and did want to get an autograph so we headed back down to the dugouts from the stadium side and Maurer was still signing autographs & taking pictures with the kids on the field. Mark and I waited for another 10 minutes & Maurer turned around and started signing autographs for the kids on the back side of the dugout too so Mark got his glove signed.

What a class act Brandon Maurer is!
This is the frame for my hammock-raft that was inspired by Little Big Town's song 'Pontoon'
It uses four 55 gallon drums for flotation which should provide about 400 lbs of flotation each.
The frame is 6' x 10', the gap that braces the barrels has an inner width of 16" and the two inner 10' boards have an inner width of 3.5" to facilitate a 4x4 post that will provide the hammock stand.
This is my first attempt at posting a photo directly from my phone.