Why not calculate drive fuel characteristics with the drive?
The 2nd generation drives in Step 6 calculate fuel mass and volume at the time the drive is designed, but they wait to Step 21 to calculate cost. Convectional drives calculate fuel consumption and wait until Step 21 to get fuel tank volume, range, and cost. Not calculating the Conventional Drive Fuel tank volume at the same time as the other specifications usually, at least in my designs, leads to not having enough space for fuel to meet the original performance specifications.
I recommend moving the fuel calculations to Step 6 and Step 7 Hyperdrive FTL instead of Step 21.