are you sure that its plastic and not fiberglass or acrylic ? there are tub refinishing kits
http://homeguides.sfgate.com/painting-s ... 34971.html
you have to sand the tub really well. also you can use oxalic acid (barkeepers friend cleaner) mixed with the mr clean with amonia. this will remove staining and help etch it for the refinishing paint.
a how-to refinish your tub . not sure what this tub is made of though
https://www.youtube.com/watch?v=PKsMXEpdefU
FROM everything i have read,and through brief experience, the main thing is getting the tub prepped for the paint, by making the surface lightly "roughed up" or sanded in order for it to accept the paint. the keyword is lightly, bc you dont want to damage the surface by sanding it too deep. washing the tub with tsp (trisodium phosphate) and follow up with a light sanding is also an option. remove any caulk if possible. then, the tub has be rinsed really well, dont leave any grit from the sanding behind, bc it will make a painted blob of mess. then dry well. (let air dry for few hours , then dry it with a blow dryer to assure complete dryness. this will warm the surface which helps adhesion of the paint (warm, NOT hot). then apply a good quality latex paint. let dry for about 6 TO 8 HRS, then for 2nd coat, paint over with an
epoxy appliance paint (rustoleum has this). most sources say let dry 8 hours after this second coat, but thats if climate /moisture conditions are ideal). i would go minimum 72 hours with a small fan on low and also bathroom vent on. when painting the tub be mindful of particles dropping onto the surface,(this can foul the job up) wear short sleeves, and prevent any hair from getting on it at all costs. if anything should land into your fresh paint, use a pair of tweezers to get it out.
if done correctly, you can expect a fairly decent looking tub (at the very best)
take care of the tub and it should last possibly a year. if not, it will end up looking 10 times worse than before.
....don't clean the tub with abrasives or harsh chemicals, only use a mild detergent such as dawn dishwashing detergent. immediately dry up any water, don't leave
anything sitting on the tub such as bars of soap or shampoo bottles, razors, washcloths, etc. dont spray any aerosols like air fresheners or hairspray near the tub.
you can paint the faucets and drain too. use a metal primer, then use a paint for steel/metal surfaces (a metallic finish looks good here).