Read yesterdays question about which barn quilt pattern you would design. My question is how do you do this? What type of base would you use to paint on that would withstand weather? Any ideas would be appreciated!

outdoor house paint

I think they use marine grade plywood

Even outdoor plywood warps in wet weather. What else could you use?

the marine grade shouldn't, that's what we make boats from

I would seal it with several coats of marine grade sealer.

sounds like it should work...

outdoor plywood, treated or marine. I also would seal it good before and after painting with out door paint. The one my sil made also has a frame that seals in the plywood edges, she glued and nailed it to keep out the moisture.