[quote=@Necroes]
I probably know the answer, but I'll ask anyway;

Would a Sister of Battle be an option? Say, Order of the Argent Shroud. The ecclesiarch would want a representative onboard, and a sister in a self-imposed Repentia would be a great guard for a priest looking to start a church.
[/quote]

Yeah an SoB is fine. Its not hard to assume that with pilgrims on board, there's probably more than one member of the Ministorum among them. My only thing would be not to make them a Repentia since that's a pretty tall order and sort of permanent. I would suggest instead they're doing a personal penitence crusade or holy duty.