For exhausr extensions on two-stroke engines, Aero-Trend markets large diameter silicone tubing. It can be used on 4s engines, but it doesn't last too long because of the heat.

For an example I've attached a picture of the right engine nacelle on my Tiggerkitty, the fairly big blue hose near the center of the picture is the engine exhaust.

Second pipcture is one engine with the cowling off, the muffler outlet goes into the pipe at the firewall.

Last picture is the engine with the beer can cowling (True!) in place.

I usually get no more than a small amount of oil on the ends of the hacelles and the underside of the stab and elevator.

Bill.