We have been running 3 or 4 training courses year since 2014 and never catch up, it is such a money pit.
We're the same, OT shifts every day of every week in my place. Power generation, outages, sick cover, holiday cover, projects, training, covering secondments... you really do write your own pay cheque.
Its been like that since the late 90's and there is no way for a company in certain industries to cover every eventuality with full time employees. Its cheaper to have a core group and cover 'extras' with OT.
I make myself NA (not available) or just say no, have done for quite a few years as I dont really need the cash (at this time) but probably moreso, cant be f%#ked ruining my days off, I occasionally decide that I have smashed the banky and do a few... reckon I did 2 or 3 after the week gap between the Deviate build and the Spur purchase, just to keep the numbers looking the same.
I know plenty of guys who absolutely rely on OT for living.