Well, the Apostolic Tradition is probably not Roman or as early as people earlier thought, but that just pushes back “baptism in the buff” to an even later date. It makes it clear that baptism is done nude:
“they come to the water, the water shall be pure and flowing, that is, the water of a spring
or a flowing body of water. 3Then they shall take off all their clothes.”
Cyril of Jerusalem’s (d. 386) Mystagogical Catecheses (which may have actually been from his successor, John) date to the late 4th century. Here’s another little snippet:
“2. As soon, then, as ye entered, ye put off your tunic; and this was an image of putting off the old man with his deeds. Having stripped yourselves, ye were naked; in this also imitating Christ, who was stripped naked on the Cross, and by His nakedness put off from Himself the principalities and powers, and openly triumphed over them on the tree. … but say with the Spouse of Christ in the Song of Songs, I have put off my garment, how shall I put it on? O wondrous thing! ye were naked in the sight of all, and were not ashamed; for truly ye bore the likeness of the first-formed Adam, who was naked in the garden, and was not ashamed.
3. Then, when ye were stripped, ye were anointed with exorcised oil, from the very hairs of your head to your feet…”
I know more evidence exists (for example, we have references to catechumens undergoing physical examinations during the Lenten scrutinies), but as I have other things to do, that at least provides evidence that in 4th century Jerusalem baptism was done naked. From various references, though, I think it would be safe to say that this was, for a few centuries, a nearly universal practice.