does it feel like your in front of a sound cannon? or inside of it? perhaps garbage can over your head?
spray foam, might work i suppose, by giving internal structural support. a high density spray foam (lots of smaller size bubbles) closed cell type i would imagine might work better. guessing a foam for a flotation on of a dock or inside a boats haul? most likely a 2 part mix.
using "great stuff red can", and trying to get a hose or nozzle shoved all the way through the frame and then getting it to fully expand through the ROPS frame as you pull hose/nozzle out... perhaps? though i am guessing you would need to let ROPS frame set bare min a week maybe a 2 to 3 weeks. for the foam to actually cure and harden. if ya tried to start tractor up before then. you may end spinning your wheels. spray foam likes regular air to cure correctly, and when put inside a pipe or like, it takes extra time to cure. i have found that out by trying to fill one of them cheap "float ring" swimming pools ya pickup at pretty much any local store. and reason for 2 part mix style foam. that doesn't really need air to expand and cure.
was going to suggest using some bungie straps. or getting some threaded rod and run just above the hinges (left to right side, and then corner up to middle top). but if ya ever roll the sucker. the ROPS' would most likely pinch at the hings and not work like suppose to, and end up trapping you or harming you.
might be worth a try, some pool noodles. there cheap, take a utilty knife and cut from outside into center. ((kinda like pipe insulation)) and slip them over the ROPS. secure with ductape or plastic zip ties?
old bathroom towels, and some ductape? wrap them around the ROPs frame and secure with some ductape. LOL. *ughs* *shrugs* worth a try?
