Mini Track is no longer offered in lengths longer than 8 feet. However, if you are looking for longer lengths, check out Screen Wall, which is available in 10 and 12 foot lengths.
Mini Track does not need to be mitered. You can cut the spline ant the end of each run, then trim the screen and it will cover and seal the corners. This is the recommended and most common way. Mitering can be done if you need to, but the spline ...
It’s recommended that you use the Mini Track square spline for the best hold but round .175 spline will work with the system if you’re using a thicker screen material.