Ok ive just plasterboarded (dot and dabbed) where my shower is going. I put a batton behind the board (in between the two pipes) where the mixer will screw to and the holder for the head. In my haste I didnt even think to put a batton in for where the enclosure screws to

Typically the dots and dabs are either side of where the screw fixings (theres 3) need to go for the enclosure so theres basically 12.5mm MR plasterboard and then a 3/4in void behind. Ie not ideal for screwing the enclosure to!

Are the any fixings that can be reccommended for such a job that spread their load behind the board? Or do I need to start cutting my lovely neat wall out

Thanks

Could you not put a few holes in and squirt board adhesive foam in there??

Can't you just use longer screws. I would go for exterior wood screws which you can get up to 4 inches long.

To be honest this shouldn't be a problem, as op's has stated just use some longer screws. The ones usually supplied are about 50mm so they should reach the masonry behind also use a good quality adhesive silicone as well and that will be more than adequate.
Plus what is the finish going to be tiles or multi-panel?

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If you think nobody cares, try missing a couple of payments..

Its gonna be tiled mate

If the tiling is going past the cubicle then this will also be adequate to fix to

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If you think nobody cares, try missing a couple of payments..

If it is siliconed and the plugs go through the tiles, then it will be absolutely fine