The problem with any crack repair is if it fails, water can soak into the floor and create an even costlier headache. And crack repairs can appear unsightly
To repair shower trays, how we did it is buy a replacement tray, angle grind the edges and overlay on the existing tray.(the original tray provides support which is often the reason for the failure....re connect the plumbing, seal around the side with a good bathroom sealant and you are back in business.....whole process takes around 20 minutes.
Some mobile home manufacturers now supply slightly undersized trays to accomodate this technique. Interestingly Trigano are one, who make CI, Roller Team and Autotrail.
Channa