Jay;

How about building a simple frame from 1” X 2” material?

1. Make the frame larger than the largest cake of interest.

2. Use screws to join the frame.

3. Stand the 1” X 2” material on the 1” side and join the four pieces.

4. You can use ½” plywood attached to the top of the frame.

This would give you strength and yet relatively light weight.

Tom