It’s likely a standard 5’ tub/shower combo. Most likely PVC.I don't think there is any "FEMA standard" tub. Various trailer builders adapt their standard designs to meet FEMA functional requirements, but the components used will vary. The emphasis is more on "cheap" than customization.
As Dutch alluded, most RV tubs are light weight and skinny, so it is doubtful that the CleanCut fixture would fit well. Their website has a Sizing Guide and a Sizing Video to help you figure out if it will work. See CleanCut Bath Cut Out - Product Sizing & How To | CleanCut