I am working on an island in 3ds max, comprised of most of the assets my studio has made over the past three years, and am trying to set up our terrain textures on the modeled terrain. I can do this through vertex painting in 3ds max and blending the textures in a single material; however, my problem is that I cannot export the non-standard "blend" material out into an FBX. I can export the vertex paint information as seen below.
Sketchfab detects the two sets of UV's, but doesn't accept more than one material, thus I cannot have more than one. The long way around this is manually UVing the entire island; however, I wouldn't achieve the blending look I want between grass, sand, dirt, etc.
Here's an example of a single plain with vertex information.