How old is your caravan? There are caravan breakers but if yours is relatively modern then the makers/dealer is probably best. There are companies that can repair shower trays and other plastic components and they may be able to do the bowl. One was featured in PC a while back I will see if I can find it. Try Coatatray, or Caravansurgeon they may be able to sort out your "bowel" problem,
Do you wash directly into your washing bowl or do you put a dish in and wash within the dish ? Have a look at these , don't know where you are but we used to use a similar company like this when I worked on the sites years ago on new build houses for scratches on shower trays and benches etc , excellent end results , these are based at the btm off the country I think looking at the map but there is different companies dotted around the northeast so a Google search may bring more off them up to. Good luck.