A bit more on the MTO usage: The Allies termed F-Lighter is really an AFP ([i]AritllerieFahrPrahame) that was a gunboat version of the MFP landing craft much like the Allied LCM or LCI conversions to LCG of various sorts.
Typically these had 2 8.8cm or 10.5cm guns and about a dozen 2 cm and several 3.7cm along with machineguns and some armor. They were too shallow draft to be torpedoed using the torpedoes carried on PT boats in anything but virtually still water (they draw about 8 feet of draft at most).
Of course PT crews found these boats dangerous opponets. You are an armed cork (the PT) bobbing about in the ocean taking on a 200 ton barge that is relatively stable with several times your armament not to mention you get 3/4" plywood for armor they have 3/4" steel plate. See who wins that match up.
What the Allies needed to do was back their PT boats up with a destroyer or two on a regular basis in this theater but, Allied naval commanders in the Med were generally risk adverse from 1943 on not allowing any major Naval units to regularly go in harm's way if it could be avoided.