Originally, I was planning on using an old shopping cart. I figured the two straight wheels in the back and the two pivoting wheels in the front would provide the most ease of movement in/out of and around my garage/driveway shop areas.
Then it struck me, I was about to toss out an old gas grill that had completely rusted out when I noticed the similar wheel configuration (that's why I don't throw away anything until it is really trash). Also, I often see old gas grills sitting in other people's trash, so they are pretty easy to come by if you need one for this or another project.
Step 1: Strip Down Grill and Fit Lower Shelf
I removed the entire top portion of the grill which left me with exactly those items.
The metal bottom shelf has a large hole to fit the bottom of the propane tank. This hole need to be covered up to make the bottom shelf usable for storage and prevent the new welding gas tank from falling through.
A 1/2" thick piece of scrap plywood was fit over the bottom shelf to cover the large hole. A smaller hole (6" diameter for the 7 1/4" diameter tank) was cut in the plywood to rest the (rounded) bottom of the welding gas tank into.
Step 2: Build Upper Shelf Assembly
Wood strips (3/4 furring) were cut to form a frame for the upper shelf. The frame was fitted at an angle to make viewing the dials on the front of the welder easier. Another piece of scrap plywood was secured to the top of the frame to form the shelf.
The front ends of the side frame rails were extended out past the front corner posts, to support a handle. The back end of the plywood on the upper shelf was cut to fit around the (7 1/4" diameter) profile of the welding gas cylinder.
The upper shelf assembly was secured to the grill upright corner posts with through-bolts.
Small flat strips of scrap wood were secured to the top shelf to fit around the short legs on the bottom of the welder to keep it from sliding around.
Step 3: Finish It Off With Some Detail Components
A length of chain is used to hold the welding gas tank in place. With the base of the tank set into the round hole in the bottom shelf and the upper portion snugly held to the cut-out in the back of the upper shelf with the chain, the tank is secure. One side of the chain is permanently secured with a piece of hardware I found. The other side uses a wing nut on a bolt for easy removal of the chain and therefore the tank.
I threw on some additional scraps of wood to make a box on the bottom shelf to hold some miscellaneous welding supplies.
Step 4: All Done
I'll probably fit out the bottom shelf with some side rails to hold stuff in place down there, maybe some dowels to slip spools of welding wire onto.
You can see that the corner posts extend up above the top shelf, to hold the tank cap and can be used to hold coiled lengths of cord, hose, etc.