White Knight 500ml White Tub And Basin Paint would be a great product to use on an old shower base if it is vitreous enamel, but it cannot be used on acrylic trays.
If you want to ensure great adhesion you need to carefully prepare the surface. There's a chance lead-based paint could have been used on the shower base, so I suggest wearing protective equipment such as long-sleeved gloves, a respirator and disposable overalls. You should apply water whilst sanding to prevent dust. All the surrounding areas must be cleaned down thoroughly and the cleaning material disposed of.
Take a 120 grit sanding sheet and scuff up the surface of the base. You do not need to sand it smooth, but rather scratch the whole surface to provide a key for the paint to bind into. Once the entire surface has been abraded, clean it down with sugar soap and rinse clean with fresh water. Allow to dry and follow the manufacturer's advice located on the packages for application.
I've used this product to rejuvenate an old bathtub that had multiple layers of lead-based paint. It was in terrible condition with flaking and powdery paint. This product has worked exceptionally well and I am very impressed with how it has held up.
The White Knight paint is not suitable for application over concrete. If the floor is bare concrete then it would be a relatively easy task to tile the surface and we have a fantastic range of tiles to choose from. Alternatively, you might like to consider installing a pre-fab shower base.
When dealing with sheeting in a shower recess there are a few different types of surfaces. If the sheeting was installed within the last 10 years it is possibly a laminate or it could be an acrylic sheeting. If it is a laminate then they often have a highly water repellent surface and this can also be an issue with the paints. If the sheeting was installed in the '60s, '70s or '80s then there is a good chance that it is an asbestos-based panel and you won't be able to complete the sanding process required for the paint to adhere.
If the panelling is acrylic or laminate and you can ascertain that it is not asbestos-based then I would recommend sanding as much of the glossy coating back as possible. This will ensure the primer and paint has the best chance of sticking to the surface. You might like to do a test section in an inconspicuous place before committing to the entire bathroom.
I've yet to run into a paint product that can withstand total water immersion and be indestructible when bleached and extreme cleaning is applied to it. - redracer01
I did a shower and while it isn’t completely perfect it is 100 percent better than what it was. I just wish I had time to give it a third coat but paint is only viable for 36 hours. I even painted the drain which was chrome and pretty rusty. I used metal rust proof paint and it came up really good. - Max1