Modelling Terrain in Blender

hi all, is there any way to use the terrain script (for painting textures) on my mesh made in blender? i've tried by splitting the mesh in two parts, than i've assigned a material for both meshes. but that's simply so ugly! I've tried also to paint from blender selecting some faces and assigning them a material, but the line between the two material is almost worst than with the first method. also with assets like terrainPaint, no chances. can someone please help me??? THANK YOU SO MUCH! Z171

p.s. the mesh is a terrain, i can't use the built in terrain gameobject because of the terrain structure, it's a double side strange-shape island p.p.s mayybe another option could be changing the shape of a terrain gameobject, what abou that?