Hi Chempat,
My grandmother was Maggie Brown who married her cousin Thomas Williams.
There is a specific section for Travelling People, where I also asked a question.
https://www.rootschat.com/forum/index.php?topic=813727.0There someone provided me with a link. The website was made with Flash software, so you may have to accept it, before opening on your computer.
http://romanygenes.com/evans-family/4571213814 It will take you to the Evans page, but there are others in Wales and England. I quickly looked in Wales and at some England pages, but that does not mean they were not travellers. It may be best to ask a question on the Travelling Families page of Rootschat, as those who frequent it have much more experience than I do. I now have further information relating to the Evans family of travellers that I will pass on to romanygenes.com.
My interest in Daniel and Aaron Evans, travelling-folk was to close that generation in my family tree. Daniel married my great-grandmother Martha Jane after her husband another Thomas died in 1917. Arron Evans his son married Martha Jane Williams, her daughter six-months later in 1918.
In the 1939 Register I could find all that were still living, apart from Daniel. My great-grandparents were married in 1894, Haverfordwest and my grandparents in 1915, Merthyr. The Williams family were Hawkers, so fall into the same category, and company as Travellers, Basket Makers and Coopers.
The closest in Wales seems to be the one you offered: Marriage between Isaac Morris and Catherine W Evans . Oct-Dec 1929 . Swansea, Glamorganshire . Volume: 11A . Page: 1907 . Line: 6. Even on Free BMD, this is the only marriage in England/Wales 1928-1932 between Isaac Morris and an Evans. If this is the right marriage, its certificate should provide his occupation and his father with his occupation. I would take a gamble and purchase the certificate. A family of travellers could be easier to trace. I only realised the Evans family were travellers, having found them in the 1911 Census living in the yard of a public house and he was transcribed as a Stowman (typo Showman).
Other than the 1939 Register, there are the local newspapers, but the online resource only goes up to 1919. As my interest was a generation or two before, I found so much about them, though mainly attending different Courts for fighting. Still I do not know what happened to Daniel and probably never will.