Certainly there's potential there for siege-sized weapons. But even smaller (yet still too large for one fubarnii to carry) weapons would do great for helping protect caravans or settlements from devanu raids or the like. I could see a howdah-mounted "swivel gun" as a perfect escort guard.
Actually, I can see a lot of potential for howdahs on a belan - gun mounts, transport for rich merchants or important officials, and later on, siege-tower-howdahs (siege-howdahs!)
I noticed that some fubarii have "binocular-goggles" - do they work well? Are they common? Certainly they "could" be used to introduce slightly longer ranger weapons - just to give a bit more tactical options.
I would certainly envisage any of these things we're talking about (artillery, longer range weapons, etc.) as very rare, very expensive (point-wise) and prone to various mishaps (explosions, belan stampeding, etc.)