The tune isn't listed in Simpson's British Broadside Ballad and its Music. The two copies of The Great Sea Snake in the Bodleian have no tune specified (and the tune is not given for any other broadside there).
Folk Songs of the Catskills says that the The Wonderful Crocodile had the tune of the Great Sea Snake specified, so perhaps it's a version of one of the tunes for that.
The Rakish Rhymer (1917) specified Rampant Moll for one of the songs there though.
JCs tunefinder shows no entries for that title. Nor are then entries for it in Levy or LOC.