There apparently is another thread on this same topic currently running.
But, at least in the case of the 13 footer, SCAMP
didn't just "Add" the toilet/shower. It was two different options that were made available in different degrees in the standard and deluxe at slightly different times.
If you are shopping for one it looks like mid to late nineties were about the earliest appearance of these options. , if it has the large front window, it doesn't have either option. Tell us more about what you are wanting to do and more help will be forthcoming.
In those later trailers my WAG is that less than 20% have the bathroom and even fewer have the shower option.