Another option is to install Swagelock tube fittings on the ends of the tubing. You can go from straight tube to pipe, or AN, or various other connections depending on the fitting used. These come in stainless steel and when properly installed (key statement here), the connection pressure rating is equal to the tubing itself. These are generally designed to work with ~0.035" wall tubing. Here is a SS 3/8" tube to -6AN adapter fitting:
http://www.swagelok.com/PRODUCTDETAI...e=&CTSCKey=189
Not cheap, but these are precision made high quality industrial grade fittings. The -6 tube adapter fitting above lists for around $11.00 each, which IMO is very reasonable considering the material and quality.