Vertex Color Shader

Hey guys,

for my game I created all assets with Qubicle and exported them with color as fbx. At the moment I use I custom shader I downloaded to get access to this colors. Now I want to overlay a dirt texture on these colors but I can't get it to work.

I found some of Unitys expamples and tried to modify them.

I got it kind of working but the texture is moving when moving the camera:

Shader "Custom/CustomShader" { Properties { _Color ("Color", Color) = (1,1,1,1) _Detail("Detail", 2D) = "white" {} } SubShader { Tags { "RenderType" = "Opaque" } CGPROGRAM

     #pragma surface surf Lambert

       struct Input
 {
     float4 color: COLOR;
           float2 uv_Detail;
     float4 screenPos;
       };

 fixed4 _Color;
      sampler2D _Detail;

       void surf (Input IN, inout SurfaceOutput o)
 {
     o.Albedo = IN.color.rgb * _Color.rgb;
         float2 screenUV = IN.screenPos.xy / IN.screenPos.w;
     screenUV *= float2(8,6);
          o.Albedo *= tex2D (_Detail, screenUV).rgb * 2;
      }
   ENDCG
 } 
 Fallback "Diffuse"

}

I found another solution, using a bumpmap but that doesn't work on the house, on a cube it works perfectly...

Shader "Custom/CustomShader" { Properties { _Color ("Color", Color) = (1,1,1,1) _Detail("Detail", 2D) = "white" {} } SubShader { Tags { "RenderType" = "Opaque" } CGPROGRAM

     #pragma surface surf Lambert

       struct Input
 {
     float4 color: COLOR;
           float2 uv_Detail;
     float4 screenPos;
       };

 fixed4 _Color;
      sampler2D _Detail;

       void surf (Input IN, inout SurfaceOutput o)
 {
     o.Albedo = IN.color.rgb * _Color.rgb;
         float2 screenUV = IN.screenPos.xy / IN.screenPos.w;
     screenUV *= float2(8,6);
          o.Albedo *= tex2D (_Detail, screenUV).rgb * 2;
      }
   ENDCG
 } 
 Fallback "Diffuse"

}

Shader "Custom/CustomShader" { Properties { _Color ("Color", Color) = (1,1,1,1) _BumpMap ("Bumpmap", 2D) = "bump" {} _Detail("Detail", 2D) = "white" {} } SubShader { Tags { "RenderType" = "Opaque" } CGPROGRAM

     #pragma surface surf Lambert

       struct Input
 {
     float4 color: COLOR;
           float2 uv_Detail;
           float2 uv_BumpMap;
       };

 fixed4 _Color;
       sampler2D _BumpMap;
      sampler2D _Detail;

       void surf (Input IN, inout SurfaceOutput o)
 {
     o.Albedo = IN.color.rgb * _Color.rgb;
          o.Albedo *= tex2D (_Detail, IN.uv_Detail).rgb * 2;
           o.Normal = UnpackNormal (tex2D (_BumpMap, IN.uv_BumpMap));
      }
   ENDCG
 } 
 Fallback "Diffuse"

}

The textures I'm using are just some random textures I found in my project.

Can someone explain what I'm doing wrong? Please help! Thanks!