look through the econolight website a little deeper they have all kinds of shit there dirt cheap! I've been thinking about putting another 175 watt mh in there but I think Im gonna take it slow I still have a shit load of cfls so If I need extra lighting I can throw a couple of those in the cab....... the cooltube is about 3.5 inches around and 13 inches long..... you could use this
Coleman 288 Lantern Globe at REI.com too its cheaper and its actually made for light to pass through Im sure this would help with any lumen loss aswell