109 Rock Sliders

The 109 has very vulnerable sills.  There is next to nothing supporting a 2" deep aluminium panel which runs from the bottom of the front wheel arch to the back wheel arch, just under the bottom of the door.
With the Kauri Coast Safari looming, and the promise of some difficult "challenges" to be tackled during the 5 day adventure, I decided to make up a set of sliders along similar lines to the set I made for the Range Rover.  I also needed to protect the LPG filling point which poked out under the sill.

  "The 109 has very vulnerable sills ......
   ..... I also needed to protect the LPG filling point"

The first step was to remove the original sill panel (the flimsy alloy bit), and see what was available on the form of mounting points for the new slider.
Removing the original sill revealed only one solid mounting point.  This is a flat section of steel approx. 30mm wide and 40mm high directly below the door hinge.  It's position is perfect for mounting the front end of the slider.  For the rear end, I decided to make up and extension from the rear chassis outrigger which would bolt to the outrigger and be welded to the slider.

The slider rail is made from 50x50x3mm galvanised RHS.  This is plenty strong enough for carrying the full weight of the 109 should it belly out, provided the mountings are strong enough.
I cut the sliders to length, continuing the line from the wheel arch.  The ends of the sliders were capped and then the sliders were clamped to the vehicle to enable the mounting holes to be marked out, and the outrigger extension measured.

Three 12mm holes were drilled through each slider, one in the front end to match the mounting location under the door hinge, and the other two at 900mm centers.  Two small mounting plates 40x50x6mm were cut and drilled to 12mm and welded to the main body support steel work to match the holes at 900mm centers giving extra support.  (This is probably an overkill, but I always tend to over design)

The outrigger extension was cut to length and welded to the slider.  To mount the extension to the outrigger, two plates 100x100mm were cut - one from 6mm plate and one form 10mm plate.  The 10mm plate was drilled and tapped with four M10 bolt holes, and the 6mm plate was drilled with 11mm holes to match.  The 10mm plate was welded to the outrigger and the 6mm plate welded to the slider extension.  This means that the slider can be easily removed should the need occur.

The result is extremely sturdy, and will more than cope with the riggers of hard 4wheeling. 
In the end I decided to completely remove the LPG filler and re-pipe it to the rear of the vehicle, just above the rear cross member.
My only complaint was that the sliders sat out 40mm form the bodywork.  Great for panel protection, but not great for the aesthetics.  Easy solution - fit some Flexi Flares!