I had mounted my Halotron Fire Extinguisher back in May '04 using the Stable Energies steel mount that attaches to the front of the passenger seat. While it was perfectly OK with me, my girlfriend was always getting purse straps, etc hung up in it and it dug into the backs of her calves. It wasn't long before she hated riding in the shark, mainly because of this. The obvious solution:
So I had her sit in the seat while I checked out the area, also I had one really tall guy and a very short lady from work try it out. It seemed like it only needed to move a half inch or so down, if I could just do something about the stamped steel clamps that stuck out, catching clothing and digging into calves. Below is a pic of the mount showing the white vinyl tabs on the latches that snag on everything. They could have been pounded flat to alleviate the issue, but that would have compromised my ability to get to the extinguisher in a hurry.
This is a reference pic that I took while I was going through the initial head-scratching on this project. Compare to the "after" pic below.
Here are a couple of views of the solution I came up with. It's basically a SafeCraft bracket with some standoffs and an aluminum plate that I had my machinist brother Jon whip up for me. Notice the trick lightening hole in the center.
The idea here is to utilize the Stable Energies steel mount after trimming it a bit shorter, with the standoffs fitting up inside the channel. Here I am eyeballing the mount to see where exactly I want to mount it and how much of the steel channel I need to trim off. I still have the old bracket in place at this point since I needed it as a visual reference. Up to this point I had not been taking very precise measurements, but trying to account for where the seat was closest to the mount and where I felt everything needed to line up, with a built-in fudge factor such that I would have some room to adjust-to-fit. Still, I had to take into account the height of the old bracket above the mount channel, the fact that the SafeCraft mount sits even higher than the old bracket, and the possible interference with the front edge of the seat, etc. It's great having a brother for a machinist, but when he lives 300 miles away you have to either have an exact design worked out up front, or as in this case, get measurements that are "real close" and rely on the fudge factor.
With all of the figurin' and head-scratchin' done, I positioned the aluminum plate where I wanted it and used it as a template to mark and drill the mounting holes.
Next I marked and cut the mounting channel, smoothing the edges carefully with a file. As you can see from the scuff mark between the holes that I drilled, about 3/4" forward of the rear pair of holes, the seat actually touches the top of the mount. As it turned out there was ample clearance between the edge of the seat and the hardware that protruded through the hole. I had miscalculated a bit, and the bracket had to be mounted a bit further forward than I expected, because the extinguisher needs to remove rearward just a bit to disengage from the bracket. This is where the fudge factor comes in -- I had originally planned for the edge of the seat to rest about midway between the bolt holes.
That's the chance you take, eyeballing things in-place when you don't have the time or inclination to tear it all apart and figure everything to the nth degree. 
Here it is, all assembled on the bench...
...and with the mount attached to the seat.
I ended up with the result I wanted though -- from the top, it's a very clean-looking install(IMHO).
Overall, the extinguisher only sits a little bit lower than before -- the difference is just under an inch -- but since there is no clamp mechanism on the top side, it's much more comfortable for the passenger if they do happen to rest on it. Also, the design of the SafeCraft bracket allowed me to rotate the extinguisher so that the handle is down out of the way where it won't catch on clothing either.
And yes, I did think of debris falling into the nozzle. I found that an old-style plastic Kodak 35mm film canister lid was exactly the same O.D. as the nozzle. I cut a 1" length of bicycle innertube which goes around the nozzle and film can lid, holding the lid in place. It hasn't fallen off in well over a year of use, and I tested it by removing the nozzle from the extinguisher and blowing into it with some canned air. The lid popped right off and flew about 20 feet, so I'm confident that in a panic situation, If I forget to pull the lid off it won't impede operation at all. I love it when a plan comes together!
Here is a comparison shot so you can see how much lower the mount is now.
Might seem like a PITA for something I hope to never use, but it was well worth it IMHO... now the only thing that the girlfriend hates about riding in the car is that I won't let her smoke in it...
