Is it permissible to fast two days a week for life, this being a vow I made while traveling?

It is permissible for you to fast a vow while traveling. Fasting while traveling is permissible for whoever is not harmed by it, whether the fast is obligatory or supererogatory. If fasting becomes difficult for you and you are harmed by it, then it is permissible for you to break the fast, and you must make it up. If you break your fast while traveling, you must make up the day you missed, because it is a fast specified by a vow. The Hanbalis are of the opinion that you must offer expiation in addition to making up the fast, for failing to observe the specified day's fast, but the relied-upon opinion among the Shafi'is is that it is permissible.