I started building one with a buddy a couple of years ago who had a utility trailer at his buddies shop but I could never get them together to finish it so I built a UDS myself. Then another lol. You should make sure your tank wasn't galvanized before starting as it is very dangerous to cook with galvanized steel as it releases bad stuff (zinc?) when heated. Other than that, I think the water tank would work better that the UDS as the steel is a thicker gauge and will retain the heat better with less bleed thru. My idea was to have the larger tank as the cooker and we had a smaller one which I wanted to lay horizontally below and to the rear plumbed to the cooker via 2 or 3 heat exchangers with dampers. Have fun and don't foget to post pics of the build as we all love pics on this site!