Most repairs will be unsightly and just a temporary fix. If appearance is not a problem, Bondo makes a repair kit.
3M Indoor Living - Bondo #20186 Tub/Shower Repair Kit
Replacement depends on how the current one was installed. If it is easy to get the surround off, it's not that difficult to remove the pan/tub and replace. If they were screwed, glued and tattooed on, it may be a major project. The key is a direct replacement to negate the need for refinishing the area. You may not be able to get the surround off without cracking it so you may need to replace both. Below is a source.
http://www.pellandent.com/RV_Product_Categories.aspx