The root end of the wing cradle is a piece of 3/4" plywood cut to 36" wide by 24" high. Approximately 3" in from each side, 1 ½" deep by 8 ¼" wide notches are cut for the wing spars. A 1x6x36" is attached on the outside, and it abuts the bottom of the notches for extra support (I don't believe this is necessary, it's just nice to have).
A single 2x4x8' is all that holds the two ends together length-wise, although there are three 45-degree diagonal 2x4 supports on each end.
First I made an "I" shaped frame out of the 2x4x8' and two 2x4x36" slabs. Next I cut the horizontal 45-degree supports, squared each end of the "I" frame, and screwed the diagonals into place. Then the 24x36" plywood ends get screwed to the "I" frame, squared up, and the vertical 45-degree 2x4 gets screwed into place.
Here's the view looking outboard.
The outboard end...obviously has nose rib shaped cutouts, and I stapled thin carpeting to the cutouts for scratch protection (not really padding).
For padding I used a large sponge and some bunched-up acoustic foam jammed under the leading edge. It crushes to the form of the leading edge and seems to work well.
If you want to make the cradle into a castering dolly, what I did was I added one more 2x4x36" on each end, to which I bolted the casters.
My advice to you is to get some nice, large, rubbery casters. The ones I used are kind of cheap. They get the job done, but a little extra shock absorption goes a long way when you're wheeling this thing around.