Joe,
That is the way the dealership that I worked at was and that is the main reason that I left. When the work was there, the required 45 hr week wasn't bad when you were turning 50-75 hrs a week. I turned as many as 130 hrs one week (in six days) and set the shop record for the most hours turned in one week. That was a great plan when there was work but like you said, if there wasn't any work, there was no base pay so it wasn't uncommon to turn 30-40 and still have to be there the full week and a sat every 3 weeks. I always wondered how "legal" it was to require us to work hours that we were not paid for. Since I am the only tech here now I pay myself flat rate because its the easiest for me to figure for now. When I get big enough to need more help, I will have to change that.