I've heard of this and seen it work, but today's bottles do not have the solid plastic base of yesteryear. You can use a 2-liter base as long as you have good air flow for engine cooling and obviously plastic cooling. They will melt away if to close to the engine, and what a mess that turns out to be. OR you could use a 2-liter bottle as a form and wrap with 1/32 to 1/16 plywood and use fiberglass for the front of the cowling.

If you decide to go this route, get a fresh bottle of soda/pop, as they have high pressure, soak the plywood to give it some flex, usually place wood in a plastic ziplock bag with enough water to soak into wood. Let the wood soak for about 1-2 hours or until you can flex it. Take the wood out, let dry slightly, just until it turns a light/dryer color and bend around the 2-liter form (don't forget to wrap the bottle with Saran Warp, as this keeps the epoxy and CA from sitckin to the bottle), expoxy, and hold with rubber bands and/or tape...once you THINK it's ready to remove, shoot with some thin CA, let rest and carefully remove. Again, let set for 1-2 hours, and your ready to go. Maybe...This can be a very tedious and time consuming skill project, but well worth it.

P.S. I gave you the Readers Digest Condenced version of instructions. Please think thru, and plan ahead.