Im sure it will fly pretty well on a D12 or even a E9. , or if you got another , and fibreglassed the tube , glassed the fins , and made through the wall fin slots. You could get away with a Aerotech E30 Blue Thunder
But you would be better of Rocsim'ing her before she flies , just to make sure she is stable , and if you need to add any noseweight.
You dont need all the glassing of the tubes or fins if you dont want to. I did mine up with a 24mm mount. Ran it through all the engines working my way up. 18mm C6-5 first with an adapter, then C11, D12 then finally an E9. All went well!
I did however drill a few holes in the body tube on the fin lines so that when I glued the fins with epoxy they would anchor in. I used about 4-5 coats of sanding sealer then painted it (though glassing the fins is a lot easier, just takes longer).
Rocsim showed it would be stable with the added weight of the E9. Also I used twice the tube length of shock cord and put a 15" Nylon chute.
I had another Patriot with the standard 18mm mount that I stuck a 18mm Aerotech RMS D13-7 in. Now that was way cool! Talk about a "Bat out of H***!".
My next Patriot project is a 2 or 3 18mm cluster. I'll try to post some pics.
It's a nice looking rocket that isn't so small you loose it and the $8.88 price tag Walmart has it for helps!