I have suggested in the past that an excellent product to use as hides and caves is ABS drain pipe, available in various sizes and easily cut to desired lengths. Being black, it's also less visually obtrusive than white or grey PVC, but as
Fishman Dave
mentions, it apparently floats in many areas; all the ABS I've ever bought or scrounged in Canada has always sunk; I'm sure the gummint has some obscure "buoyancy laws" that the makers must obey...
If you use PVC, there are apparently some spray paints that will adhere to it and are non-toxic once cured. I think
FINWIN
has some info on this. When I've used PVC in the past, I've found it helpful to spread a bit of clear solvent cement over the outside of the pipe and then roll it in, or sprinkle it with, aquarium gravel; it blends in very nicely and looks less artificial that way. Be sure to let it cure thoroughly.
Whatever you use, after cutting it to length you should at least use a sharp knife to de-bur the sharp jagged cut edge inside and out, or better yet a rasp or file to smooth it.
That's a gorgeous fish; do whatever it takes to make the tank suit the fish, rather than hoping for the opposite.