Well that's interesting; the values are not 0 - they're just really tiny (Ie, 0.00000000000165083106). Do the same process again, except this time use modview (Pof editor>model>MOI) and copy-paste all values from the 9 text boxes. If that works, then it might mean PCS2 will need the precision of its editor turned up.
It's more likely to be something else though. If the mass is comparable to a similarly sized capship, then the only other thing I know of that could have an effect is the $Density: field in the table entry, which should be 1.
Oh, and make sure that you're deleting the IBX cache file between each change you make to the pof file.