Fitting concealed shower thermostat

[Paris Farm]

I've purchased a minimilist concealed thermostatic shower valve from Victoria Plumb, the instructions are basic and its not clear how best to securly fix the unit. There are some screw holes in the brass but they are not easily accessable, and there are no suggestions as to how this should be fitted into a stud wall. Any ideas as to the best way to secure the unit or if there is a fitting kit available?
Thanks!