Your heater usually has a metal box with knock outs where the flexible hoses hook to while routing to areas of your trailer. Though they are usually a larger diameter than what you would need for for your project. You should be able to find smaller diameter flexible metal hose and accoutrements to mount to that plenum at the home stores. IIRC, a bath room vent fan uses the smaller hose, and there are kits to install those with just the hose and such. I used dryer vent hose to extend a vent into the bath of my trailer. Use the better metal hose if you are extending outside to the elements, as mice can chew through the cheap stuff.....
