An idea for riding dinos with weapons. Try something like the skyrim horse mechanic. it should cover pretty much anything you should need for it. Consider not allowing RPG's while riding dino though....
Have you ever considered adding attachments to saddles? Is there any reason why a saddle cant hold say, a torch?
To build off of that, I wonder if it would be too much to make it so some saddles on some dinos can have guns attachment to them. Say a ptera with a couple of assault rifles that are pointed right forward. Dogfights with dinos anyone? For added bonus, make the head the targeting retical.
Add harpoon guns, and ichy saddles with harpoon launchers?
just some thoughts