The cannon volley gun sounds like it would be an absolute riot once it's loaded with special cannonballs. One acid cannonball is ded killy, so obviously more would be even killyer right? Maybe two cannons, one in each 'hand' slot, so you could follow up one special cannonball with another?
The 25mm field gun sounds like it would end up as "Armored Car but worse" and I can't see it being that great on the battlescape. Might be a good fit for Male Touch, but I'd still rather just have an actual A-Car. Rather, for the lowtech 2x2 heavy weapons platform niche, something like the ratman reaper cavalry might be fun. Get a Reaper Cav, swap the rotogun for a 25mm autocannon, put a Lok'Naar (peasant? slave? gal?) on top, and there you go. Heck, just get the Gal Hyena Rider and give her a cannon.