Mate,
The simplest "mod" I have seen to stop reflected gravel from the trailer hitting the rear glass was a piece of 5mm thick corrugated plastic "cardboard" type stuff trimmed to shape and stuck in place with 3M "Protector" easy-peel adhesive tabs on each corner.
As for the tailgate.... same thing but with extra tabs as required to fit the contours of the tailgate skin. (it will fit under the lower edge of your glass canopy window, allowing for easy opening and closing of both and making a better dust seal!!)
Ok, so it blocks out ALL vision through the rear window (but let's be honest... who the heck uses that mirror anyway?)
The most expensive bit is the 3M mounts.... about $20 from Bunnings.
Easy to fit/remove, cheap as chips and no damage from drilling, screwing, silicone or 100 MPH Gaffer tape needed!
Hope this helps. (Well.... for the next trip anyway!)
Graeme
OR... you could try this....
http://www.obiesoutback.com.au/obie1.htmEDIT: P.S. My missus just came up with one she uses too..... A couple of $5 windscreen sunshields from anywhere that sell them.... One on the glass (outside) & and one on the gate (outside) held in place with Gaffer tape....
LOVE IT!
MY15 MN GLX TRITON Diesel Dual cab with a few bits and a never ending list.
"If that's all there is my friend, then let's keep dancing.
Let's break out the booze and have a ball."