I've gone off castors even though I do offer them on the cabs I build for customers if they really want them.
They are a great source for rattle I've found and are frustrating when you load into tight areas.
In addition, having castors on your cab means you don't get full floor coupling which can amount to a few dB.
Far better, in my opinion, is to use what we call here "Hand Trucks"
There are many types, sizes and weights and with a little forward reasearch you can find one that is easy to take along with you.
Stretchy cords help hold more than one cab in place whilst carrying on the hand truck.
Great for stairs except those where you need two people and castor would be un-useable anyhow.
Mo