[JoeUser]

First thought I had when I saw the title of the thread was "Man, that's gonna really hurt..."

Seriously, though, I can't think of any easier way to stash a chainsaw than putting it on the rear cargo mat and using a bungee net to hold it down. Chainsaws are such an irregular shape that you'll probably have a hard time finding some specific mounting clasp. You'll have to fashion your own custom solution, I'm sure...

 

[JoeUser]

Here's an idea: Look into those M-Pac slotted panels that mount in the rear panel area, or on the inside of the rear door. You could thread some small ratcheted straps through the slotted holes and secure the small chainsaw that way.

Also, I would find some sort of leak-proof bag to store the chainsaw, to prevent chain oil from dripping all over the inside of the FJ...