If you have a silicon flex pipe to attach muffler, then no worries about heat transfer back to engine.
may want to spray inside of muffler compartment w high temperature automotive paint to protect the wood.
ive run a completely enclosed canister behind a DLE 55 engine for many flights without issues.
cooling engine is all you need.
baffle the engine w 6mm thick foam from Creatology that you can buy a sheet from Michaels Craft store for $1.
easy to trim w hobby knife and glue w CA or hot glue. It’s heat resistant too.
khoi