I think this is fantastic. I was exhausting all possibilities with the previous parts. However.. Besides some issues with some things loving to break without provocation, I think some of the sizes are a bit off. For instance, the big orange fuel tank. If I want to have two of them side by side, lateral connectors needed makes a huge gap between them. Also the double connectors, I think they should be the same gap that the triple connector has in base KSP. They are SLIGHTLY larger. I really wanted those lateral connectors to stablize things, but if you snap it under two fuel tanks, for example, it only actually connects the top of it to one of them. I'm sure this isn't your fault, though, and it's just that KSP itself isn't checking for another joint for the top to connect on. edit: I also forgot to mention that the large boosters tend to rip things apart when they start. Maybe it's from the g's suddenly stopping, or their weight even when empty being too high.