I've always just washed my convertible tops with regular car soap and water, but I know there are allot of other 'convertible top cleaning' products out there.
I know this might sound goofy, but go over to www.corvetteforum.com and go to the car care section. I don't recall the exact name of the product, but I know there is a ton of information on cleaning and maintaining the water / weather resilience of convertible tops there.
Just don't make the mistake I made. I always use a cotton washing mitt to wash my cars. I ran this over the convertible top - left a layer of lent over entire roof. It took me an hour using a lent brush and tape to remove all lent and return to baseline! Learned my lesson - less is more!
If it is an 08 it should'nt really need cleaning and proofing yet, unless it lives under a tree.
Turtlewax do a 2 bottle kit one a cleaner and then a reproofing agent, I used it on my smart roadster softop, but only after the car was 4 years old, I just squirt a hose over it everytime I wash the car, they recommend to not put a car wash wax on it so I just use cold water and if there is any marks use a sponge to clear marks.
The material they use for the softop seems to keep looking good as I have had mine almost 5 years and it still looks brand new.