Any reason why you couldn't use DOT-5, silicone fluid. Do be careful about DOT5 fluid it may not be hygroscopic, but that doesn't mean water can't be a problem. I've seen a few cases of water collecting in bubbles in the fluid. If it boils, no brakes. Also it seems to defy the laws of physics that a liquid is not compressible.
Pedals get spongier as the fluid gets hotter.
Not a great thing in a heavier vehicle like a pickup. I think it's great stuff for show cars and other low use vehicles, but have had ample reason to very leary of it in real life. Anyway, I've used DOT 4, usually Castrol. No failure for him yet, but in my case, my pedal went to the floor. I usually get that as well.