Element extinguishers are an excellent safety update and super easy to mount... they come w simple clamp bracket (included in the package) which u could zip tie to rollbar. I've mounted one in every vehicle, my boat and in each of my trailers. No expiration, works on all fire types and super compact - pricey compared to traditional canisters but they are super effective and very convenient as well as safe.
Anywho... u want extinguishers EASILY visible and more importantly EASILY accessible. Suggestion would be to get some 3M double-sided (red) trim/body panel adhesive tape and mount in passenger footwell against center console (you could just use a sheet metal screw too)... or for that matter, since so compact, in driver-side footwell against console so even closer just in case...
Good luck
