So for jump ships, it's not worth it to build any smaller than your jump drives.
Yep - I usually pad my jump ships up to the drive's "size" with fuel tanks.
One clarification - Aurora rounds ship mass (other than fighters) up to next integral number of HS, so you don't need to worry about the ship's size being a fraction of a HS too small.
For example, let's assume you haven't researched any of the "small" systems (like small fuel or small crew quarters), so the smallest system you've got is a 1 HS fuel tank. Let's say you've got a jump drive which can handle 120HS (this used to be my standard jump drive). You then go to design your jump cruiser, and end up with it saying that its mass is 119.3 HS (the fractional HS will be due to armor). That's ok - 119.3 gets rounded up to 120, which matches the jump drive.
John
PS - glad you got some use from that post - it turned out I was wr...wrr...wrrr...wrong about what was causing that particular player's problem.