Possum board

I am wanting to make a possum board for my dulcimer. First of all, I am not an instrument builder but have built some decent simple furniture.

Several questions

Is there a possum board specific pattern other than the dulcimer?

How thick should the wood be for the bottom?

How high above the possum board should the instrument sit?

What do you use where the instrument contacts the possum board to prevent scratches to the finish of the dulcimer?

How do you finish the possum board?

Thanks. I look forward to the advice the wonderful friends on this site will provide.