I just built a quilting board to go over my sewing machine cabinet yesterday out of MDF and it is working wonderfully. The cabinet normally holds my Kenmore but she has been acting up lately and my Bernina does FMQ much better. So I switched them. But the Bernina sits up higher then the Kenmore did. I needed to raise up my surface just a half an inch.
I bought a half inch thick x 2x4 foot piece of MDF in the precuts section at Home Depot. I did not want to mess with the big piece. The piece I got was not too heavy and is easy to manage. When I got it home I drew out the cuts I wanted and my husband cut them out for me. He used a fine blade so the edges were smooth. There needed to be two pieces. One for the basic table overlay and then the smaller piece in the front where the bobbin is. I kept it really simple.
Then I covered it all in light batting. I had fusible that I use for purses so I used that. Which worked great because it did fuse to the board. I had to cut it where the hole was for the sewing machine. I taped it on the back. I could have stapled, but MDF is hard and I also did not want staples scratching the cabinet top. After the batting I covered it with fabric. Then I covered the whole thing with plastic. I used the fairly heavy stuff, I think it was called deluxe weight at Walmart.
The only problem I ran into was the front inset piece was too fat. So I had to take it apart and take out the batting. I wanted it to be tight so it would not wiggle and the plastic seems to keep it stuck in there pretty good.
I think it turned out pretty well and does not look too silly. I did some quilting on it last night and it worked really well. I used to plastic, not to keep anything clean, but so the quilt will slide around easily.
I don't think moisture will be a problem here. But I was planning to make a top for my ironing board using a similar technique. I had not thought of moisture effecting the MDF though. I was thinking of using insulbrite. But would that have enough moisture protection? I was thinking about using the same size, 2'x4'. But I was also thinking I would have my husband add two strips of wood on the underside to keep it stable on the regular ironing board. I was even thinking of attaching webbing straps on the underside to keep it from falling. Sure do not want that thing crashing down on my foot. Oh well, a project for another day.