tis not ship scale weapons, i've mounted a pair of 25MW laser guns. they get a UCP of '+', not much use via the UCP system, but not all that bad via the normal system v armour of '40', well if ya get a HIGH PEN result anyway.
i tend to mount a couple of guns on most ships like this, anti-personael things mostyl, here the main weapons battery.
I'd go for a battery scale weapon mounted ala fixed forward arc, actually i don't see the problem with doing it. not see it written anywhere the only difficulty is the size of the weapon. i tend to assume 50% of turret volume.
Essentially a tripple laser turret ISN'T three lasers in aturret, but one tripple power laser. thus still works out at 50% volume no matter what. the other 50% is the turret itself.