As anyone ever stacked more than 2 I was thinking a 4 gallon gas, a blue kerosene and also the black storage. Can three be stacked? Pics if so. Thanks.

 

A 4-gallon gas pack is double wide and would require a universal mount plate on top of the Jeep wheel mount. Then you could fit (I believe) up to two more on each pack mount, depending on the mount type, for a total of three per side.

This JK has three stacked but they look to be all 2-gallon packs.
All J Weekend 042 | Flickr - Photo Sharing!

The Rotopax Flikr account has plenty of examples and you can see the 4-gallon pack on the back of an ATV.
Flickr: rotopax.com's Photostream

 

I think I will go with this setup but just mount a blue and red like this. Can't you interlock with plastic clips?