Auxiliary gunboats were used by the germans during WWII in a great variety . This is the MS Louisa converted into such a vessel . These vessels were used for security and convoy support.
I haven’t thought about the armament jet, but you could definitely mount a 88 mm gun in the central position and 37mm or double 20mm guns fore and aft and an additional 20mm on top of the wheelhouse . I will put some Warlord weapons on it when i did the mould.