This is my first post here. I apologize for the length of it. 
When I read the instruction booklet, it said to “fully tighten” the MDF slats with the socket head cap screws. I did this, and at first, the screws were not very deep into the slats, even though they were secured to the bed and were flat (as MDF usually is). So I tightened them all to completion.
Now I am a bit worried, as each slat is slightly elevated.
I am fairly certain that the bed is now uneven. I can of course remedy this by fastening another 3/4" sheet of MDF to the top and surfacing. I had written a parametric spoilboard OpenSCAD file for my 3018 a while ago, and while I was waiting for the Shapeoko 4 XXL to be delivered, I amended it to fit the hybrid table. So I can at least go that route.
I have yet to do anything with the Shapeoko 4 XXL except to initialize / home the machine. I plan to do another look or two to be sure that the frame is still square, belts are adjusted, etc. I loaded up cncjs on a spare RPi4 and got that ready to rumble.
Should I loosen all of the bolts fastening the MDF slats until they all lie flat on the table? I imagine the slats will just drop back into place. As I said, I still plan to add an additional spoilboard on top to keep things “safer” if possible (less chance of a bed crash perhaps).
One more question: when I cut the spoilboards for my 3018, I blue taped / CA glued two boards together, cut one side, flipped the two boards and did the other to prevent bottoming out. This would be heavy with 3/4" mdf and I’m not sure I’ll be able to find 1/4" in an XXL size (but I will keep looking or perhaps make 2 separate boards – I have coded for this already).
Thank you for any help or suggestions!