Despite all the nay-sayers out there, I have a QT in my sump.
It is a 3g jug (plastic jar originally containing pretzels) sitting in the sump that happens to be just large enough to accommodate it.
By default, it comes with temperature control since the jug sits in DT water.
I fill the jug with the DT water and siphon out old water into a separate bin. -When done with the QT the fish will be well used to the DT water and with the every-other-day 30% water changes in QT I also change the DT water. (I use the water twice). Of course the QT water never directly contacts the DT water.
All I really needed was the jug, some PVC piping as 'furniture' in the QT, and a small air pump.
IMHO it can be done.