Unfortunately, PP is the worst for gluing, sanding, and painting.
PE (and in its variants of HDPE, LDPE, PEX) is worse than PP for gluing and painting, in my experience. But PP is a close second.
However, you could use bolts, use sticky tape/decals or fill it with resin to create a plug that has an undercut - and attach things to the plug.
You could also try a paint that envelops the part and holds itself together, like Plasti-Dip does: thick acrylic has worked on PP for me because it did so.
I have heard that flaming it can temporarily change the surface tension to allow better adhesion - this is sometimes done industrially to allow decals to stick better.
Good plastics for props:
* PET (1), plastic bottles. Works fine, but not often you find it in a useful shape.
* PVC (3)
* PMMA is acrylic.
* PC is polycarbonate. More impact-resistant than acrylic. Not suitable for laser-cutting from what I have heard.
More unusual: PC-ABS (PC and ABS blend), PBT: you find them mostly on equipment that need to be durable. PC-ABS is like ABS, PBT is very hard and can sometimes have a ceramic feel to it.
BTW. PP is the material used for drain pipes in my country, but for some reason they are often labelled "ABS pipes" - I suppose ABS is an acronym for something else than the plastic
in this instance. Very confusing. I built my very first prop out of a PP tube ...
The only place locally where I have been able to find any assortment of PVC pipes and fittings for water has been a store that caters to salt-water aquarium enthusiasts. There is some use for cable ducting though. ABS plastic don't seem to be used in house construction over here.
