There is a water soluable stripper that I used on a couple of exciter tunnels that I have. It works awesome. I bought it from Napa and its about 17 bux a can. Basically you brush it on, then use a bondo spreader to remove the finish. Some times you have to use a little bit of 0000 steel wool to work the trouble spots. Hose off and you have a clean tunnel. Whats nice is that there is a coating on the aluminum that will stay clean and nice looking if you are careful with the steel wool and wont require polishing if you would rather have a factory, clean looking tunnel.