We have them in school and just use PVA, undiluted. Spread the glue on the plastic liberally, allow to get tacky then offer up, there isn't much scope for re-aligning, but as they're angled it's easy to get the right height.
All I do for painting them is use a fine grit wet 'n dry just to take the gleam off, clean with a decent detergent, allow to dry, ready for painting. Simple.
If you need to remove them in future use a long-bladed kitchen/carving knife. We find they don't get knocked off at all, I presume the PVA has a certain amount of give in it, but they can be prone to people (kids) picking at the edges, so I now also run a thin bead of decorators caulk down each edge and smooth it over with a wet finger.
For PVC, the old solvent based gloss top coat applied directly (no undercoat) was as good as you can get, as it solvent-welds itself into the surface of the PVC (you can't even wipe a splash off). I haven't tried it with the newer low volatile version, but a test run might be in order.
Our house had these when we bought it, it was used as a care home for many years and had wheel chair bashes all over the place. They looked like plastic angle sections made for the purpose, and were stuck on with double sided tape. Some had been painted with the same emulsion as the wall they protected.
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