I prefere an inline layout as opposed to the side by side. Fits better in narrow spaces but need More pull to lift up. The rear mount fuel will be nice to move, but will be more prone to toppling over especially while changing the Oxygen bottle, will likely mean removing your fuel bottle (propane) your handles aren't my favorite but are pretty standard hand cart design. You could consider cutting down a standard hand cart(?) preferably with the hoop handle.That will not address the wheel size mentioned above bigger is WAY better than the little 10's those come with. My fire stick kit came with a cart, 5" wheels, not fun if you run over a big piece of dust, a pebble means two hands [with a single grip on this cart]. This should be replaced, one day, I hope. Tool box/shelf needs to have a tall back so as not to self empty every time you move it, and in accordance with GJ fashion, bigger isn't enough! As alluded to above adding a tie-off is an excellent idea to help keep her upright. Harry
P.S. a bigger tube diameter [@ the appropriate length] will help to not cause the hose to take an inconvenient "set," also consider a squirt bottle and fire extinguisher as availability/projected need arises!