there are RC parish records for Dun Laoghaire on the Irish Family History Foundation Website at
www.irish-roots.ie (South Co. Dublin section)
Kingstown/Dun Laoghaire births : 1755-1900 marriages : 1755-1900
there is a marriage for a Bridget Hanlon in 1852 Co. Dublin, Dun Laoghaire Parish but there does not seem to be a match for William at that time.
(its a pay site - €5 per transcript, the index search is free)
Tully church looks like it could have been in Ballybrack Parish, which has baptism records on IFHF database but not marriage records, these may be included in the Glasthule records.
Shane