I carry tubes on flights for work all the time. Karl's canvases should roll up well and fit in the overhead easily. I've never been charged for it . . in fact they've never even counted it as an additional carry on. You can get tubes at a local Kinko's/Fedex . . . and get some tape so the end caps stay in place.

I also have around 5 or 6 of Karl's paintings and recommend him.

As with any such transaction negotiate/confirm size, price and delivery date as much as possible up front.