A while back, I noticed this in the Endecker G-wagen catalog...
They were using adjustable rail tie-downs from "Mac's tiedowns". It seemed simple enough and appropriate for the G so I decided I'd do something similar. (as I wrote this up, I realized I need to add some more pictures)
Here's a quick shot of the interior with the tailgate track in place.
The track replaces the trim strip along the tail gate floor. You can also see the single point versatie anchor on the wheel well. I have one on each side.
On my first try at installation, I had passed the bolts through the floor with lock nuts under the truck body. This turned out to be problematic because it made complex work of removing the strip if one ever wanted to peek under the rear mat to check the tank sender. The track also turned out to be too close to the rear door so I was forced to re-do it.
On my second pass at it, I decided to go with rivnuts. These are aircraft grade zinc plated steel fasteners that are a little tricky to install correctly (without the proper tools) but make great "blind" threaded anchor points.
The result is a track that replaces the trim strip and is easy to remove as needed.
What you don't see is that I've also added one of these tracks to the rear face of the back seat bottom. There, I drilled and tapped into the approximately 1/4" of steel frame. (I need another picture here). Additionally, I added Land Rover D-rings to the upper rear seat mounts. I considered putting versatie mounts there too but the D-rings are so easy to install using the existing bolts.
So now I have a load space with plenty of tie points around it. for day to day stuff, I just run a bunch of bungee cords criss crossing so I can put bags, boxes etc in the gaps and nothing slides around.
for trips, I have cam straps that can hold down all the bulky stuff to prevent any shifting.
Oh, and for the kids, these make great "LATCH" connection points for car seats.
Link to mac's site
(Also thanks to Craig Reece for giving me the single mount pieces.)