Like everything else in this hobby/business, everybody has thier own way of doing things. Tube design is merely getting the parts you have/can get together to do what you want. Baffle design is just like any other scope - the object is to baffle the light and the procedure is the same whether it is a newt or a refractor. Optics design books are available from Willmann-Bell and software is available on the net. G-sum is a quick and dirty program for doublets and OsloLite is good for detail work. Good luck and ask if there is more.