First things first

I was about to pick up my first bottle of argon and realized I had no safe way to transport it. So I stick welded a bottle support for my trailer using my new PowerPro 205 and some old bedframe steel,
so I could safely strap the bottle to it. The welder in stick mode is much smoother and controllable than my old Lincoln tombstone unit (which is for sale by the way). I was able to do some successful practicing with the tig last night on mild steel. Not so good with aluminum, :O but I blame myself for not preparing the surface sufficiently. So far, I'm very happy with my purchase! :D

Looks good....but why not just lay it down???

You could have hauled that home on the flat, even acetylene can be hauled on the flat but is not reccomended due to the possiblity of solvent loss, so I haul that in the upright. A good workout for the PP205 on stick, it is smooth and easy to control these inverter DC rigs. Main thing is to secure the bottle in any position.

Right, only acetylene needs to up upright. Years ago I was told acetone would eat up o-rings or something. So that is the only think that is vertical or almost 100% vertical that I haul. Don't let the DOT see you without the safety cap on there either. $5000 fine here.

I have a Jetta of that same generation and folded down my back seat and slide the bottle in on its side. I do like the idea of the rails on the trailer though.

Yea I guess I could have fit the 100 lb bottle inside, but was a good excuse for welding something up, and I didn't want to dead-lift the bottle into the trunk. Plus I plan on using the rails as the beginning of a bottle rack for my welder cart, which is why I bolted it to the trailer. Just need to make a little shelf for the bottom and some hooks for chains to secure the bottle.
The Jetta is a TDI and has 308,000 miles on it, and I've pulled some serious cargo on the 3000# rated trailer (gently).