I just got the Front Runner 10gal tank that fit in their two jerry can holder. Nice, but big. I'll set it up for three mounting positions, which will vary dependng on the load out, but in all cases include the jerry can holder for secure mounting. For just me and the dogs for a weekend of fishing it'll go in the rear cargo area, mounted to a plywood floor, which will mount to the tie down points. For a bit heavier load out, on a rack that mounts through the spare tire, supported by a ratchet strap to the AEV tire carrier post. For heavy load outs, on the roof rack.
There is fourth option I'm looking at and that is on a Synergy cargo area rack, which is rated for 500lbs and mounts high, to clear a fridge, etc. But I'm awaiting the rack and won't know how it will work until I get it. The Synergy rack is frightfully expensive, but the only option I could find that mounted high enough to clear a fridge and stove and still allow use of a soft top. You can purchase just the brackets and fab a basket to save some $'s
I have the AEV bumper and that water will be clean up/dogs, etc. Non-potable, since there is no easy way to clean the tanks.
Link to Front Runner tank - TexasTJ has one of the two ~13gal tanks on the page I linked, don't know which one:
http://www.frontrunneroutfitters.com/Water-Solutions-c47/
Link to Synergy cargo area rack and brackets:
http://www.synergysuspension.com/Synergy-Suspension-Jeep-Wrangler-Baja-Basket-p-18614.html
JPK