You can buy a Tailgate Storage Lids from Wagon Gear in the US. No idea what shipping would cost. This mod is a copy of the Wagon Gear Lid, but is cheaper, more time consuming and a little agricultural!
This isn't a full write up, it is more just to give 60 owners an idea of another mod to do on a rainy day.
20mm steel angle was used for the frame. The latches were purchased from a local boating shop. The tailgate was lined with RAAMAT body sound deadener to protect it. Handy hint.... don't store anything too heavy in it as it does make the tailgate quite heavy. Items such as snatch straps, rope, garbage bags, belts, tyre deflator etc are ideal for storage in this space.