I guess if I use 5 or 6 of my "straight edge" 2x4s on top the layers, with lots of weight on top of that, it should hold them flat while the glue drys. The router table top itself being already flat would be perfect for setting it all on.
My reason for going without an insert is to avoid leveling problems. My intension is to have the two flat surfaces (table and fence) within just a few thousands of an inch. Joints should require minimal planing or sanding to be perfect. I understand I may have sag issues with a 1/2 inch (plus laminate) MDF, but I can always add a support under the router's base to hold it up tight, since I don't intend to be removing it much. The Triton has a full 5/8 inch clearance above the base which means I can change collets or bits in place. Even if I add a 1/4 inch hardboard surface to that (for large bits), I can still get the included cranked neck wrench on the collet.
I disabled the the automatic lock-off when the collet is raised, so I don't need to get at the router controls. I can see only two reasons I would need to get under the table. To adjust the speed control, or to lock the plunge...both of which would be required for large, say raised panel, bits. I'm putting a glass door on the front, for viewing when I'm bored.
Just in case I am not satisfied with the router's power, I also intend to make the hole in the bottom layer (3/4 MDF) a 1/2 inch larger than the 2-1/4 HP base, so I can switch to a 3-1/2 Triton later.
My fence will have a micro-aduster and dial indicator (Pat Warner style), and inserts in the fence to fasten subfences to.
I should have nbeen an engineer!
Mike, I have edited my profile a bit.