To keep board flat, get an archival box the size of the board and store your board in that. If your board still warps, put the board in a plastic bag and then put the wrapped board in the archival box. This will take up no more space than just putting the board under your bed. And the board will definitely stay flat. We can supply the archival box and include a free large plastic bag. The board, too, if you want AlphaRag ArtCare. We would ship it to you in the box.
Michael A. Smith
Lodima Archival Materials