this is what you need:
- standard movement tray (like the ones from GW)
- a cheap dry erease board
- usual tools like glue, scissors etc
- disassemble the dry erease board, take the metal sheet (usually it's very thin) and trow away everything else. Be careful since the edges of the metal sheet might be sharp!
- using some scissors (I used some kitched scissors like the ones used to cut the chichen's bone) trim the metal sheet so it can fit the tray
- glue the trimmed metal sheet on the tray