Kirkhill: I would think that a commercial design utilized in the role for which it was designed is not on its face (or in practice less safe) or somehow otherwise inferior in design to military specifications, these are simply different specs for different applications. While there can clearly be some common shared characteristics, all the rest is apples and oranges. A naval vessel designed to military standards is not necessarily any safer than a commercial ship if it is pressed into a commercial role or a role that does not require at a minimum standard the design of a warship. Even liberty ships, as great a design as they were, were not built to a true naval standard, yet if any piece of equipment could be said to have been the decidingingly most influential mass production design in WW2, it was such a vessel.
Not many liberty ships sought out the enemy - I believe they prudently avoided the enemy at all costs despite their armaments. Similarly, hybrid ships such as armed trawlers performed minor escort roles, often ending in disaster. Purpose design warships sought out the enemy unless a tactical reaons held them back. The primary reasons would be proper armament and probability of the design to survive an engagement. Therein lies the primary distinguishing characteristic between commercial and military design standards.
On the matter of crew size - the Canadian Navy [like all Navies] uses a time tested watch keeping system that keeps a vessel at a certain state of readiness, depending on the anticipated situation or transit status. It follows that the smaller the crew size, the more time each crew member spends time closed up at their station rather than performing training, maintenance, crew rest etc. This is sustainable only for a short time, perhaps a few years at most in time of war, before the crew reacts negatively.
The key seems to be able to crew the ships to a military standard, keep them floating and fighting after suffering some battle damage, and in the case of Canada to design them to be adaptable to a plethora of diffuse accommodations standards and changing technology over a 40 + years lifetime (in both offcial languages and one or more spirits)