Here are a few more pics:
First off, this was put together rather quickly so nothing pretty. For the two kegs in the front, I just roughly cut a piece of 2-in rigid foam for them to sit on. Mainly just to raise them up a bit as the can narrows at the bottom and they were a little tight.
I needed to bridge the gap between the two "fenders" on the inside where the wheels are so the back keg would sit on something solid. I just cut a 2x6 to fit.
The last step was to secure the regulator as high as possible. I found that the #5 tank we are using fit perfectly inside 5-in thinwall pvc. The conduit here is electrical but I believe the white plumbing variety may work as well. I happened to have bell ends for this conduit. I used these to strengthen the ends a bit as the thinwall is not too sturdy by itself. Couplings or male adaptors would probably work just as well. After cutting to length, I drilled a few holes at an angle through the bottom bell and screwed it to the 2x6.
The tank slides in and is supported by the tube between the regulator body and tank. If you dont like this system you could probably just add a block of wood inside the conduit to hold the tank off of the regulator entirely. If you plan to use a smaller cylinder, I am sure you could find a piece of pipe of the appropriate diamater.
Also, as you can see in the last picture, I did not have a manifold. I used two 1/4-in tees and soldered them together with a piece of 1/4-in copper tubing. There is a check valve/pressure relief right off the regulator.
I need to add a drain. I was thinking of using a picnic tap (as I have a few that I no longer need) on the back between the wheels. There is a nice recess here where it would be well protected.