I wouldn't get overly fixated on whether the rent will cover your mortgage. Right now, you have to pay a mortgage anyway. You are adding a rent bill to your outgoings. You are adding a rental income to your cash inflows. There are some adjustments in your tax situation, but the basic calculation is whether the rent you get will be more or less than the rent you have to pay. Of course there is a risk that you will be left without rent; But if this goes on for any length of time, the important thing is to be able to bail out of the lease in Cavan ( so you should look to negotiate this in your house lease).
Incidentally, there is a huge surplus of rental property in Cavan:- I suspect it may cost as little as €500\month to rent a house up there.