This may not help if it's strictly 1798 that you are researching, but here goes just in case.
The discharge papers of an ancestor state that he enlisted into the Elgin Fencibles on 1 November 1799, when that regiment was passing through Gloucestershire. Clearly, they were then on their way to Ireland, for after arriving there he volunteered from the fencibles for the 72nd Foot at Newry, County Down on 5 July 1800.
I hope this adds something to the picture.
Ian