In my stockish FJ40, I have stored my 4' Hi-Lift in a couple different places. One is spanning the width of the tub behind the front seats, and the other is my current favored location ratchet-strapped lengthwise along the driver's side fender.
Neither are very accessible, but I have not found that on the trails I've been on that quick access is very important.
I thought that to have it inside would help keep it clean, but in an FJ40 everything gets dirty anyway, and it would probably be better to keep it somewhere where I see it more often and can get to it to clean it easier.
I would mount it the way Ricardo and Martin have theirs mounted if I had side steps...