Tiling a bath panel can really make a bathroom look great, but it can cause problems especially if leaks occur under the bath at a later date, if possible you should make provisions for an access panel just in case you do ever need to gain access under the bath.
External plywood is often used in such applications but is not ideal for this application as wood expands and contracts, therefore you are much better off using tile backer board. This can be Aquapanel, Hardibacker, Wedi board, Lux board or any number of tile backer boards.
Aquapanel and Hardibacker are more freely available and are both cement based and can be cut with a Stanley knife and straight edge (you'll get through a lot of blades) or buy a £5 a saw and accept it will be not much use afterwards.
Build a frame out of 2x2 inch timber or 3x2 inch timber, remembering to allow for the thickness of the tile backer board, tiles and bed of adhesive.
Do Not PVA the surface before tiling.
Tile the bath panel as you would tile a wall remembering to leave an expansion gap.
Remember to leave an expansion gap when fitting the tiles or else the grout will soon crack.
The gap between the bath panel and floor can be sealed with silicone sealant.
