All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
It is permissible for the person whom you mentioned in the question to combine two prayers with one ablution when travelling. The fact that he suffers from incontinence [of wind] does not matter, because one ablution is sufficient for a person who suffers from incontinence when he combines two prayers. This is whether he combines the Thuhr and ‘Asr or Maghrib and ‘Ishaa' at the time of the first prayer [i.e. at the time of Thuhr or at the time of Maghrib], or at the time of the second prayer [i.e. at the time of ‘Asr or at the time of ‘Ishaa']. Thus, he may combine two prayers with one ablution and he is not obliged to perform ablution for each prayer.
Ibn Qudaamah said, “It is permissible for a woman in menses [that exceed the normal course] to combine two prayers with one ablution. This is because the Prophet ordered Hamnah bint Jahsh to combine two prayers with one Ghusl (ritual bath), and he ordered Sahlah bint Suhayl to do so as well. The same thing applies to women who (have blood discharges and) are not in menses and women who have other excuses.”
For more benefit on the ruling on incontinence, please refer to Fataawa 172327, 163887 and 152651.
Allaah Knows best.