FamilySearch has a few possible baptisms for William Wellings around Ellerdine; could any of these be your man ?
William Wellings baptisms:
21st October 1787 Cressage, Shropshire
Parents  William Wellings, Mary
21st September 1788   Great Bolas, Shropshire
Parent Ann Wellings
4th August 1782 Shawbury, Shropshire 
 parents  John Wellings, Susanna
Regards,
Maurice