I built my own drawers, with a 850mm slides. I reckon its as well made and as strong as as the commercial ones. (might not look as good though). I primarily built the drawer system because I wanted a fridge slide to sit on top of the drawer. The slide because it now was elevated had to be a drop down slide, but as you can imagine it not cheap.
Now that I have the wisdom (a little bit), here are my thoughts.
1. You dont need drawers that slide out on runners, simple pull out boxes would be better.
2. If you have a drawer, you loose space and increase weight. Also something more to break.
3. The fridge slide can be made redundant if you install a gullwing window. i.e. access from the side of the vehicle. This saves a lot of useful space on a defender, especially if its on the right side.
4. Although I built my own drawer system, I had fun building it, but the cost savings over buying one was not much. Also took me longer.
Next time.

