you'll find the info you want
here in the errata
the bit you want is the 2 sentances just above the
miscellaneous heading, which i'll repeat here for convenience;
"heavy weapons teams are supplied with a large base to contain both crewmen and weapon. treat them as two seperate models that are based together for convenience of movement."
this tells us that there 6 single wound models in a heavy weapons squad and
not 3 multi-wound models.
hope this helps.