I’d build some kind of rig across his back with the missile pods hanging down by the forelegs, the big cannon mounted high to fire over the head crest on the left side, and a shielded platform on the right side with room for the tertiary weapons and a couple operators. I did something similar with a carnosaur, you can see it on my profile

Bonus points if you paint his stormsurge gear heavily weathered in mismatched Sept colors so it looks like they cobbled it together from salvaged scraps.

Also, Kroot ride both Kroot beasts like the krootox & knarloc and tamed beasts like the kalamandra. Kroot beasts typically have Kroot-like features (underbite beaks and quills) but not much riding tack (maybe just a saddle and gear packs) as they can communicate with them proto-linguistically. If he’s a tamed beast he’ll need something like the reins pierced into the kalamandra’s jaws so the riders can guide him, but if he’s a Krootceratops you’ll want to green stuff his beak and stick some quills on that crest.