Thanks for the comments everyone. I have been considering different ways to make the map more natural and have even tried restarting the whole thing on the natural ground, but it's really proving difficult given that the bunker goes underground. Unfortunately, this re-skin won't include high ground.
Have you seen a High Ground remake by the name of Timber Shore? Not exactly a High Ground remake, but more of an inspired-by. Anyway, he used the terrain of Tempest to make his map and I gotta say the terrain looks pretty darn good. It's at a slightly too steep incline, but with some trial and error you might be able to make it work yourself. Just thought I would throw that out there since you're thinking about using natural terrain. Great map by the way though : )