Years ago, Four Winds replaced my shower under warranty. They took part of a day and the finished job looks like new. Based on that, it can't be too big a job providing you can get at the plumbing.
There have been several threads by people rebuilding their RVs. That includes the showers.
Probably depends on your DIY skills. Hope it works out well.
Class C, 2004/5 Four Winds Dutchman Express 28A, Chevy chassis
2010 Subaru Impreza Sedan
Camped in 45 states, 7 Provinces and 1 Territory