Make sure to use Epoxy, (not polyester resin), and plan on a good heat shield around the exhaust. A small blast tube would be even better. composite will work but remember it sits above 1600° Exhaust. Tracy runs a simple separator plate under his plywood box so it should be safe, but take no frivolous chances. Fire in your engine compartment is very bad mojo. I have seen one so I may be more sensitive than most.
Bill J.