Blast launchers are already the weapon system with the lowest crew requirement, but I'd argue they shouldn't require technicians (maintenance personnel) at all. I'd like to illustrate this with an example.
What's the crew requirement of a can of tuna? This seems ridiculous, but this is the question I'd like to ask about blast launchers. They are a sealed system (ammo is already in it) with no moving components not requiring any power beyond a 'go' signal that are single use. You don't do any maintenance on a sealed tin can. Cracking it open would do more harm than good. It's hermetically sealed and therefore its contents are preserved. Some components such as nukes might degrade over time, but simple maintenance while underway wouldn't fix this. Instead, I'd expect them to have an expiration date.
Therefore I propose that blast launchers shouldn't need any technicians at all. This would halve their crew requirements.
It's also odd how 10 Blast Launchers having each 10 cells have 10 times the crew requirement of a single Blast Launcher having 100 cells, despite the total number of cells and moving components being equal.