As someone completing an MA in History on the Soviet history (53'-91') I would really love an exception on the modern politics ban(specifically 53'-91'/94) because the post-war USSR was so different from Union under Stalin, and the Khrushchev/ Brezhnev/ Gorby governments.
For now I will avoid discussing my favorite era of Soviet history, and delve into the one sort of under discussion, even though tropes of the post 53' USSR are slipping into the forum (leaky reactors, monuments constructed post 53')
Firstly, in response to the free trader campaign, I believe that there would actually be a considerable capacity for this sort of activity even in a pseudo-Stalinst or, certainly as previously mentioned, a NEP inspired MTU polity. The grey economy was thriving in both the NEP and Stalinist periods, and I can offer a useful historical example, that of the Soviet railway and its enterprising conductors:
Railway conductors travelling along the length and breadth of the Soviet Union had access to many local markets, and were always first to know local prices. They would use this information to either buy locally cheap and then sell higher at a later station where they knew the price for the given good was higher, or simply sell or barter the knowledge to a broker at a different station. That can correspond to a free trader pretty easily, as the crew of potentially a state-owned vessel actually make the majority of their profit off of a smaller amount of goods transported alongside their state mandated cargo. If you're going for a more NEP approach they might not be wholly state owned to begin with, and then they can functionally trade as normal. In a situation like this, knowledge of local markets is the determining factor in profitability, and therefore DMs may be added based on what the crew knows of the local market based off of previous NPC interactions. Also, purchasing not from the state-trade board, but from the grey market and through grey-market brokers may be a fun way to run things, especially if locating the supplier/broker can become a mini-adventure in itself.
To contribute to the aesthetic discussion, here is the positively gorgeous M62 diesel locomotive of the state railways.
As far as the economic discussion is concerned, Soviet style dependability and redundancy could provide a positive modifier to maintenance cost. If playing with Trillion Credit Squadron, HG, or other naval building rules this could affect the overall naval posture. To balance the cheaper maintenance, ships would need to be ordered in larger batches, and newer versions would have to be by% iterative designs. Prototype vessels would not gain the maintenance bonus, only mass-manufactured vessels would. Under these conditions a 10% bonus could be applied. For a further 10% bonus, you can start risking the vessel's integrity and then we get into risking a disaster every 6 months. On a 12+ the ship suffers a catastrophic issue and takes a given amount of damage.