My numbers aren't matching theirs, but that's always tricky since the errata changed things from what they were doing. Some of the practical details are bad - I don't see any provision for sand cannister storage other than the 12 ton cargo bay, I can't make sense of the missile storage (a battery round for 4 50 dT missile bays should be 100 missiles, not 4, but maybe that 50 dT magazine serves both missiles and sand cannisters), the lack of energy weapons or a meson battery is a problem given the way weapons damage is distributed in the combat rules, the screens are weak - but that isn't going to affect it as a way of evaluating mass.