[SG] vehicle fire combat question

I have a vehicle with a heavy weapon and a SAW, and I want to fire at a 
single target.	Do I use one action to fire the heavy weapon and the SAW

together, rolling three dice (the quality die, the firecon die, and the
SAW 
support firepower die)?  Or do I have to use two actions, one to fire
the 
heavy weapon, and one to fire the SAW?	The first option seems right
based on 
the way infantry fire works, but the 'adding support firepower' rules
refer 
to infantry only.
Thanks,
Jed Docherty