when I take the shelf out like today for a trip to the tip, I get to hear even more great tunes from the exhaust lot more noticeable. thinking might stick some sound deadening on it underneath for those cruising trips like motorway where bit too noisey and droney at anything above 50mph, might be a real improvement.

Yes, been thinking the same regarding the boot floor, something to dampen the panel resonance. I wonder if carpet on the back of the rear seats helps too, most cars these days are carpeted on the back

I've already done boot, those rear seats are might thick and heavy ! carpet might soak some up though, definitely will order some more deadening stuff and do under shelf, I'll order some shortly. Other option too would be to take the inside panel off the tailgate and sound deaden inside that (if it's possible) and put it back.