Can you get the surround off the wall fairly easily? If so, the repair is straight forward. From the back, reinforce the crack by applying some stick on fibreglass mesh used for drywall repairs-comes in a rolled up strip about 2 inches wide, like tape. Then use epoxy (make sure it works for plastic) applied over the mesh, fairly wide and thick. Or, RV shops sell a type of repair glue (much like epoxy) made especially for RV plastic fixtures. Comes in almond or white. This stuff sets up pretty quickly, so work quickly.
If getting the surround off is a pain, you could use the RV repair glue from the front side (without the mesh) and sand it down. With care, it should not look too bad. If it does, you could spray paint the repair with Krylon Fusion plastic paint. I did a few repairs like this and the paint colour was very close to the factory plastic tub.