Awright mate - From one scottish mark to another - i do this all the time - what is the material ?- watch out for laminated mdf ,needs sealed after cutting - also i always seal any wooden ones.Fix a batten along length of bath and tile up to it,leaving a good 25mm plus above level of tiles,this will then let u screw into it after cutting,use coloured screw covers to match in with panel or chrome /brass collars to give it the professional look-customers preference.I would silicone bottom as well to stop water ingress from bath-finishes job and should match in with seal around perimeter of floor.

Tofee