anon wrote:
Doh, as I read my message I realised I'd missed out info. i'm
planning to use thise little plastic supports with two holes in one
direction and one in the other. I forget what they're called!

OK, same sort of approach applies.

You need screws that will go through said little square plastic things
and then as deep as possible into the wardrobe side without any risk
of going right through.

I've used them quite a bit and, if I remember right, I used 3.5mm x
25mm screws for fixing to 18mm contiboard. I have some 4mm x 25mm as
well which are useful if the 3.5mm ones pull out.

Mount the blocks so there are two screws in the wardrobe sides.

Do a test first somewhere that doesn't matter to check that the screws
*don't* go right through.

--
Chris Green