Repaint shower tray

[JBR]

We have a walk-in shower which, although about twenty years old, still works perfectly. Unfortunately, the floor of the tray has begun to wear and the white finish has begun to wear away in the middle of the area. We were advised to paint it with exterior white emulsion, but although (under advice) we didn't use it for a couple of days afterwards, unfortunately there are now a couple of places where the paint is falling off.
Any advice would be helpful. Should we repaint using a different type of paint, or any other helpful advice please?

 

[Wayners]

Just stick a new tray in.

Was a thing for prisons and hotels where they sprayed shower trays and baths but it don't last forever. Needs to be redone every few years.
You can buy enamel spray paint. Wet and dry sand for a key. Really good clean with meths. Masking. Warm spray can in hot water and paint.
I couldn't be bothered. If it's worn then time to replace imo

 

[opps]

Who on earth recommended masonry paint?

 

[JBR]

Marge has now said that she'd like to remove the shower cubicle: tray, glass, and even the tiles (which are in good condition), but keep the shower head and controls. I'm just keeping quiet for now in the hope that she'll forget all the cost and disruption!