How can I remove rust stains from my plastic bathtub?

My bathtub/shower is orange and just yucky looking. I have an old double-wide, so the tub is made out of a plastic material that isn't smooth. It isn't fibergl but I'm not sure what it is. I have well water and the softener/filter system broke and we are saving money to replace it. I can't afford to replace the tub at this time and bath fitters won't install in our home because "it isn't supported enough". I have used commercial stain removers like Iron Out but they make me very sick even though I covered my mouth and ventilated the bathroom as well as I could. (exhaust fan, open window and additional fan blowing out.) I have tried the vinegar but it didn't seem to work that well, though it did remove some but the amount of elbow grease needed wasn't worth a clean shower. I scrubbed for almost 3 hours straight and my arm hurt for two days afterward and it still wasn't that clean. I want to get as much of the iron off as I can so that I can keep up with it. When we moved in the shower was already extremely orange. Any ideas???