[Notfishinenuf]

I think you should stay away from the wood and go with some type of composite core for a filler. I would also put in the plates as you described earlier under that core.Then I would drill a hole in the side and thru bolt the rail on as you originally thought. The hole only has to be big enough to fit a box wrench. Duct tape on the bottom of the wrench, stick the nut in the wrench and put it together. Glass over the holes and finish it up. It will out last your time with it.

Vic