I laminate a piece of G4(red fiber board)to a piece of 1/8" plywood. The G4 keeps the motor mount from digging into the plywood.
Bob

Get one of Bob Hunt's 'Hard Nose' motor mounts.  All you have to do is shape the outside to fit your situation.  The mounting and cooling holes are already machined into it.

If you are using the X-mount that comes with the motor then I think a 1/4" birch ply is the way to go.  Also much easier to integrate into the wooden fuselage structure.

If you are front mounting the motor without an X-plate then the hard nose is a good hard "forever" mounting surface, and the G10 can be prepped to be captured by epoxy.  However even with a front mount, I have made several successful installations using 1/4" ply, but I also line the mounting holes with brass or alum tubing to help resist crushing.  Again it is much easier to integrate the wood firewall into the front end structure.

Maybe he means vertical inadvertent landings onto paved surfaces.   (can't believe I got it spelled right)

I'm using some 1/8" PC board.

The way the mount is slotted in there looks like there's not much wood top and bottom so it's almost like gluing the mount to the front of the fuselage with everything forward just weight.  If that's all it takes to hold it, I've really been over engineering my mounts. Is there any hardwood in there, are you going to put blocks behind it?

MM