How to write: Poster on Frame...?

I have a poster that is mounted onto plywood and wood frame. I'm sending it Japan Post overseas. How do I write 'Poster mounted on wood frame' on the customs form?

Thanks!

I wonder if you need to write that in Japanese, because most international mail notes are written in English or French. But I came up with the phrase

木製パネル状のポスター

Maybe you can show photos of the contents and ask the people at the post office.

Thank Uco.

When I do write in English, they often don't understand and ask me for clarification, then we get stuck...