I was looking at the pics of your roll cage, before you asked about bracing, and wondering the same thing. I have an Aqualu tub as well. You’re cage foot pic had me wondering about this bracing.
Before I put the replacement tub and roll cage install, my windshield would shake at highway speeds. It was really annoying. After the install, I only get a vibration at the rear view mirror. I’m pretty sure part of the issue in the past was due to bad tires- second hand rollers. I’m running 35” muds now, so that should also cause some vibration.
All this is to say, I don’t think you need to add the bracing. On the other hand, if you’re gonna do a lot of rough driving, it wouldn’t hurt.