I recently picked up a new Halon extinguisher off eBay at a very good price and came up with what I think was a decent way to install it.
My primary criteria were to drill no holes in anything in the plane and to mount the extinguisher where both I and my passenger would be able to easily get to it.
I decided on mounting it to the bottom of the front passenger seat. That keeps it out of the way of everything, but it’s still easy to get at. To mount it without drilling holes in the plane I came up with a way to clamp a 3-inch by 1/8-inch piece of aluminum to the seat bottom.
I cut the aluminum piece to match the width of the seat frame and split the portion of metal I cut off into two pieces that were each about 3 inches long. I bent one end of each piece into an L shape then drilled holes into the L’s and mounted threaded aluminum sockets with matching screws. I purchased these from the fastener aisle at Home Depot.
I cut slotted holes into each end of the 3-inch aluminum for the screws that went to the threaded inserts and drilled and tapped two additional holes at each end. The L-brackets slipped behind each side of the seat frame and pinch down when the screws on each end are tightened. I tightened them so much that I can’t move the aluminum mounting bracket with sharp blows from a small hammer.
I then mounted the mounting bracket for the fire extinguisher to the 3-inch aluminum. The 3-inch aluminum is positioned just high enough on the seat frame so nothing from the extinguisher touches the carpet, seat rails, or anything else on the plane. The seat still adjusts easily and I can release the extinguisher with one hand without losing my sight picture over the glare shield.