Oil paint - particularly thickly applied - is NOT flexible. Rolling most paintings as tightly as we see done in this episode would almost certainly destroy them.
Boston is purportedly an expert in fine art, but he has several shinken (Japanese swords) arranged on his wall horizontally and vertically. No person with any pretension to fine art would hang such vertically, as shinken are properly stored in a horizontal position on a Katanakake. Hanging vertically could almost be considered sacrilegious.