Ballast the first few inches to foot inside the portals. Why waste your time and money ballasting an area that, it appears, will be inside of a tunnel.
On my old layout, which was fully "sceniked" (spelling?), I stopped the ballast right at the portal. You could see the foam, etc in there but I painted it a similar shade of gray as the ballast and left it. Doing it again, I'd have gone about a foot in the tunnel.
Again, don't waste time or money in a spot you won't see and that will be in total darkness.
