I don't think a "modular" or "pre-fabricated modules" to be the best way how it'd be build. In a war where you lack materials damages would rather be patched out: a ship would have things easy to fix, easily reachable electronics and such for example, easy to replace hull panels and system parts. Replacing a whole module because of some damage sounds like a waste of materials / work and would probably rather be done in case of having way too much ressources, but not enough time to fix the issue properly on ships not made to be fixed by the crew themselves.
I'd consider the two ships (freighter and transport) to be rather ships which would be "patched up" rather than have "sections or modules be replaced". So, bit more like a Junker ship, who'd rather just weld on a new Hull Plate instead of replacing a chunk of their ship with a new part.
Pre-fabricated modules just sounds like a "massivly wasteful way of fixing stuff, when you got way too many ressources anyway and only care about the product being back up to 'looking like new' status in no time". That's at least how I feel about it. Overall I feel like the ship is a more cheaply, less "fancy" build ship, massproduced, easy to fix, but not the most "high-standard" vessel you can get. Bretonia would overall more focus on fixing old vessels, considering their much fewer ressources available per lore. In the war they'd probably resort to using parts of destroyed vessels for new ships and for fixing other vessels, as far as possible.
I mean, sure, in WW2 Germany also had prefabricated modules for U-Boats, but then again, they weren't replaced to repair them, but just used to build them in different places for various reasons, like enabling them to build the ships in many locations and assembling them quickly at the u-boat bunkers.