Landing pad design looks interesting.
Been wanting to make one of them, or more, myself.
Those precut, Styrofoam rings they have in craft stores, for making wreaths would work, if you want a walled, sunken pad, for more security. Just need to apply some good, solid putty over the exterior, to get the desired effect, and to protect it from damage. Cut in a sliding access door, and perhaps add some greeblies to the exterior, and top, to add interest.
They make various sizes, so should be fairly easy to find something to meet your needs, as far as spacecraft size goes. 15mm is certainly easier, from that aspect.