In Qld the small 2 letter, 4 digit for trailers under 750 Kg, over this you have full sized plates Q something. When I re-regoed mine from 1t to 1.5 tonne, it originally had small plates but the local DOT said they were wrong and I was lucky not to have been weighed.... apparently the issuing DOT in Beenleigh had got it wrong. Remember big plate also = bigger $ rego
I think you can get personalised plates for the CT too
Paul