[Mobhack]

If the unit is a class that is assumed to be armoured, or is armoured somewhere - then it is armoured.

The AI units may well have been holding fire as they are hidden. Generally - only AT weapons fire at incoming barges and the infantry types seem to keep thier shots for when the troops dismount on the beach, then they usually open up en masse on the bunched grunts the barge has just disgorged. So that is probably a function of the barge class deep in the code.

Rubber rafts, however, the reaction fire routines will shoot up happily with rifles and mg.

Try using a rubber assault raft or rivercraft class (or possibly a light amphibian) for your modified watercraft units. The AI may have fits with inappropriate water craft, depending on the scenario. (It really only knows about beach assault and river crossing asault scenarios). Ask about that sort of thing in the scenario design forum, as the scenario design guys may have tried that sort of thing already and know what works.

Cheers
Andy