I believe Speedcoat are the leaders in this sort of repair have a look at there web site. I think they will come out to you, or one of there agents will.
But it isn’t cheap but replacing the shower tray will not be cheap, and what they disturb in the process. You can have it put back to the original colour, ours is grey, to match the cupboard door.
Our other van need this doing so I did some research, and decided to sell the van, and add this cost to a new one.
Sorry I can’t be more help.