I decided to see if I could get my 15lb NX bottle to fit in the spare tire well today.. You have to remove the jack & tire (obviously..) The bottle fits easily by itself. Mine was a little more difficult to get it to fit because of the NX remote opener, bottle heater transducer, and the blow down tube. The tube MUST vent outside the car to pass tech inspection... I'm drawing a blank as far as mounting the bottle in there. Right now, it is snug. That will not cut it for passing tech though.. The bottle has to be securely mounted. The only thing I can think of would be to use the strap style mounts, and use the side of the fender where the spare tire attaches too.. It would be a PITA to remove the bottle though... Anyone have any suggestions for mounting the bottle? For now, I'm going to either use some heavy-duty foam.. or possible a nice thick blanket or comforter... That can only be a temporary solution though. Here are some pics of the bottle in the fender:

you could make, or have made, some brackets that would mount to the side or bottom of the opening, with hinges on the backside, and bolts/clips on the frontside. That way the straps would open so the bottle slides straight out towards the trunk opening. Might be able to utilize the straps you have now in some way????

u always could go with the ol fire extengusher mount where the screw goes where the tire screw went (the one that held the tire in place) and have a little clip that holds it on like some of the fire extingushers its hard to explain so ill eather have to find a pic or ull have to guess what i mean

Well, to mount a NX 15# bottle I took an NX top bracket, cut the stand off of it, cut one of the legs shorter then the other and rewelded the legs back at a different angle so that it could be mounted to the spare tire bracket and can be opened wider then the bottle in that space. Instead of using a bottom bracket I cut out a saddle out of some plywood that matched the bottom of the bottle and the outside matched the contour of the spare tire well right where the seam where the back meets the quarter panel.

When I put my bottle in there, I used 2x2 and some 90* metal brackets to create a angled mounting surface for the straps. In front of where the spare tire goes there should be about 8-12" verticle on the interior side and I think ~6"(maybe less) on the fender side that's easy to mount to. It's pretty hard to explain, and I can't take a pic for you being 1200 miles away from that car, but it wasn't that hard, only took an hour or two, having only power drill and a hacksaw. This was with a 10lb bottle and the plastic NOS brackets. Nice and stealth with my fog light switch being the arming switch.