I am also in the business of mowing on rightofways. I took a piece of 1/8in plate that was long enough to go from the back of the front axle to the rear hitch and had it bent on a brake so it had sides that went full length. Near the rear where the filters, linkages, and hoses were, I made flanges on the top of the sides that flared out to cover any exposed plumbing. I bolted it to the loader frame in front so it could hinge down from the back. You will need to clean it out regularly as it will fill up with leaves, grass and such. With the loader on I haven't had the need for putting on tubing to protect the hood and me. Going through blackberry vines 12+ ft hasn't been a problem. I just pat them down in front while the mower is at work.
The one thing you might think of before you go out, If you are using a bush hog type of mower is to reinforce the deck and sides. I have been using mine for 12yrs and you can't hardly tell it. I have however gone through many blades and dishes. I put 3/16 plate under the top deck and 3/8 down the inside on both sides. As you know the left side takes the most of the beating. Also I use the blades that are tipped up in the back. When you hit a rock or the unknown, the back of the blade will come in contact with the deck, much better than having the cutting edge opening the deck like a sardine can. Been there.
One more thing, you might want to weld a threaded end of pipe over the valve stems so you can cover and protect them. I have had one experience of shearing one off, of course it had to be the rear,
