About to set the tray on ply and noticed the underside of the tray isn't level so the tray rocks diagonally to the tune of about 10mm. Can I 'lose' the rocking when I put the adhesive down or should I send it back (if they'll rake it !) AM I over thinking?

Feeling fed up...

You should be setting on something like wet concrete, tile adhesive etc, read your instructions - they will tell you how thick a bed you need to set it in.

Ther are no instructions for it. 

I'm using tile adhesive with a 10mm notched trowelSo can I level the base using adhesive or no?corner to corner across the diagonal it's about 10mm. My ply is bang on level!

Thanks 

Normally bedded down on mortar.

Just make sure it has a slight fall towards the trap, as power and drench showers can produce large amounts of water fast.

Hope your trap size is big enough to take the volume, as lots of modern trays only have a small upstand.

The tray would have a fall built into it,

 

Tile adhesive is perfect for setting shower trays Put a bed on the floor and on the back of the tray and level up once set it will never move 

Tray does have fall built in. And a macalpine fast flow trap.

So guys are you all saying that I can lose the 'rocking' with the adhesive? By bedding the tray on a thick bed of adhesive and tapping it down to compensate for the uneven shower underside?

9 minutes ago, Dee said:

Tray does have fall built in. And a macalpine fast flow trap.

So guys are you all saying that I can lose the 'rocking' with the adhesive? By bedding the tray on a thick bed of adhesive and tapping it down to compensate for the uneven shower underside?

Yes 

most tiles are bedded on 10-15 of adhesive