Planning to do the same myself. Assuming your taps and waste are at the bath end that you'd like to tile (as is the case with mine), I would do the following:
Build a timber frame for the long side of the bath, recessed in from the edge of the bath itself. Fix 3mm or 5.5mm plywood to the timber frame. I'm planning to use screws, as I may have to glue some of my timber frame together, rather than nailing it. The recessing of your timber frame should allow for the thickness of your plywood, tile adhesive and tiles. For this reason, I've gone for 3mm ply, as it gives me more to play with when recessing the timber frame.
For the end panel, again build a timber frame. Make sure you don't put any of the upright batons in the way of the water pipes/waste, so that you can get in to service them if necessary. I'm actually planning to have no uprights on the end panel (with the exception of the edges, of course). Measure the size of the end panel, allowing for a little bit of plywood to be hidden behind the edge of the bath.
You can now tile both panels - the side panel in situ on the bath, and the end panel independently. Be careful with the tiling to ensuring that you get the tiles on the side and end panels to match up when you fix the end panel! You might also want to ensure that the tiles on the side and end panels match the tiles on the wall.
Once you've tiled and grouted the side and end panels (you may want to use tile edging on either the end or side panel), drill holes through the tiles in the end panel and offer it up to the timber frame. You can then spot the timber frame and fix the end panel with screws to the batons. To hide the screws, use screws covers - I'm using white ones as my tiles are white.
When you're done, fill the (small!) gaps with silicone sealant. If you ever need to remove the end panel, you'll only need to replace the sealant.
That's my plan - happy to get any tips from others who have already done this.
Rich W