<<Troy, I always carry two of the small green 1# tanks under my rear bench seat.  Never though about nor care about the regulations.  I'm sure they are safe.  Many, many people are travelling around with these in there vehicles to and from stores, to and from camping trips, etc. ...>>

I was speaking more of larger, 5 pounds and up, propane cylinders. I too carry the smaller cylinders to run my coleman stove.  As to this filling apparatus for the 1 pound bottles, I saw one up on eBay for around $15. Not sure if this is a good price or not. The one interesting thing it said, is it could also be used in reverse to fill an empty larger tank. See http://cgi.ebay.com/Propane-Refill-Adapter-Disposable-Bottle-Mac Coupler_W0QQitemZ260174869061QQihZ016QQcategoryZ2020QQtcZphotoQQssPageNameZWDVWQQrdZ1QQcmdZViewItem.

If this actually worked, seems like it would eliminate the need for the extend a stay all together. Have you tried using the device in this way?

Troy