are you trying to build some sort of chiller? even plastic tubing is going to be somewhat thermally conductive. you would just have to use a little bit longer hosing and thinner hosing if you are in fact trying to build some sort of chiller. i would not feel comfortable using stainless or titanium on a saltwater aquarium.
Titanium is commonly used in drop-in chillers and some heating elements. I've never worked with it but I would imagine it's much like bending other types of metal pipe. http://www.diydata.com/techniques/plumbing/bending.php