Originally Posted by
Unterwegs
100 x 75 is 4 times bigger than the maximum size.
Sorry for being pedantic but I don't get the math. The max. size is 55 x 40 x 20 or 57 x 54 x 15 for a garment bag. So it is not even the double size but close to it. Anyway I agree that it is not easy to get the painting on board.
I agree with andre1970 that using a poster tube might be a solution. The op may want to talk to an expert though as wrong transportation can have serious consequences.