Horatio,
Yeah mate, I know, I know....wasn't having a go at you.
Was just making sure everyone was aware of the casual rate differences.
(25% is a lot, I think you'll agree to be missing out on)
WRT variations, I'd suggest either a slightly higher rate to allow for night/uniform allowances etc (Maybe $2/hr depending on workload) or lodging a pay claim at the end of each period as required?