I searched the Irish Family History Foundation's database. It contains 11,500,000 surviving rcds for abt 60% of Irish counties. The RC portions of Louth are in the database. Rcds B4 1840 are sparse. For Louth, 9 of 20 RC parishes were NOT keeping B rcds at this date. Therefore, the chance of finding a rcd for your ancestor is abt 50:50.
For Rose McGough, B 1825 +/-4 yrs, I found 1 B rcd in 1826 in the parish of Dundalk. This MAY, or MAY NOT, be for your ancestor. Hopefully, a view of the detailed rcd will show info that will validate it.
For Thomas Campbell, B 1825 +/- 4 yrs, I found 14 B rcds, 2 in Dundalk. Again, a view of the detailed rcd MAY show info that will validate it.
For possible M rcds, Louth, the only ones feasible for Rose are in 1856 & 1857. However, there are no correlated M rcds for Thomas in these yrs. There was great social turmoil and mass migration/immigration during this era. they may have married elsewhere. A quick search of all Ireland didn't show any matching M rcds on the county and yr.
Google the Foundation's name to lead you to the database. Post a msg to Genforum to tell me your search results.