Okay, I did a bit more watching yesterday of my DVDs in an effort to get a feel for relative sizes of the ships and so possibly the effectiveness of a Colonial B-25H/Mosquito Mk XVIII.
Such a ship could under absolutely no circumstances use the launch tubes. This is quite simply basic. The ribbing along the Flight Pods includes both the launch tubes and the AAA batteries. There are two launch tubes per indentation between ribs (Ref. The Miniseries and "33"), but only a single AAA turret...one of Galactica's AAA turrets is therefore at least the size of a Viper, probably closer to one and a half Vipers. It mounts two guns of indeterminate calibur, but fairly large. Call it 8-inch (203mm for you European types).
Now, unless a Basestar is significantly smaller then a Battlestar (possible based on relative apparent lengths of Pegasus and the Basestar in several places where they were in the same shot in "Ressurection Ship Pt.2"...but doesn't seem that likely) or is made of tinfoil, one of Galactica's AAA guns isn't going to be of great enough calibur to significantly damage it on its own. This means you need lots of them. Lots of them the Colonial Navy can't afford, since they need Vipers for aerospace defense and hanger space is kind of limited.
So the gun needs to be bigger then that. At least one and a half times bigger. A 12" (or 305mm) gun. And something to mount that. Now we're rapidly getting into the area of small starships, not fighters...