Well I'm headed into the second winter with my homemade cab and I wanted to make a couple upgrades. First off, I had used foam for many of the seals which was quick and easy to do (was in a time crunch at the time) but not built to last. I hit up the local auto salvage yard and pulled out a bunch of nice rubber door and hatch seals that I was able to modify to fit my cab. Seals up tight as a drum now.
The second issue I wanted to address was the tuning fork issue of the ROPS. The trans was just too loud. I drilled two 1/8" holes near the base of each pillar (You can see them in the picts below, I have little cap's that will be covering them) and one at the very top. Taking a full can of expanding foam I squirted half the can in the bottom of each pillar. Over the next 4 hours it began to come out the top hole at the top of the rops filling the whole thing. HUGE difference in sound. I know not everyone would drill their ROPS but the way I figure it, if 3, 1/8" holes will cause a failure it was going to fail anyway. Not to mention the foam can only help the structure by preventing the inward collapse of the form when stressed. Much more quiet now.
So quiet in fact, that it was time to add a stereo to the cab. I had this equipment kicking around for the last 10 years. I put a 300 watt car amp behind the seat and two speakers mounted to the ceiling. In the front of the cab I put a universal mount that holds my phone or iPod or whatever I want to use as a source. This thing CRANKS!