One way to properly prepare your artwork for the long trip is to use two pieces of firm cardboard
You then cut the cardboard just slightly bigger than the painting and place one piece at the rear and the other at the front of the painting using tape to hold the two pieces of cardboard in place.
You can surround that with bubble if you so choose .additionally you can surround that now with corrugated paper so as to create a strong well padded package
Remember to stand them on end and not flat.