Make a 1/8th tray as shown and epoxy inset into the fuz. front. Under the front end epoxy fit hardwood blocks which the engine will bolt into. My blocks totalled 7/16th in thickness. Install to allow for a few degrees of sidethrust. Then cutout front of tray to accommodate engine. I used self tapping screws with Theadlock. Fuel proof the tray. The tray top is velcroed using epoxy. Likewise the tank and flight battery bases are volcroed and the pop bottle top cover holds everything firmly in place.

The last image is my current project a 38 inch span Macs-quito.