Well - I broke down today and took the day off to buy a propane bottle. One for my furnace and whatnot. The new bottles don't drive the torch well at all due to the limited flow.
The smallest allowed by law is 15 gallon bottle. (Maybe forklifts are exempt).
The 15 is a tall sucker - I'd say 4' and between a welding bottle and a barbie bottle. The nice thing is the base of mine is a full ring - to roll if needed (tacky in cement) and has holes. The holes will be useful along with the ones in the top ring as tie downs in the truck. Horizonal transport is legal. I plan on a cradle on the side of my pickup just for this.
Martin