Writing from fragment shader into 3D render texture

Better late than never...

 Shader "Custom/Tex3DSlice" {
     Properties     
     {
         _MainTex("3D Texture", 3D) = "white" {}
         _Depth("Depth", Range(0,1)) = 0.5
     }
     SubShader {
             Tags{ "Queue" = "Transparent" "RenderType" = "Transparent" }
             LOD 200
             Cull Off
         
         CGPROGRAM
         // Physically based Standard lighting model, and enable shadows on all light types
         #pragma surface surf Standard fullforwardshadows alpha:fade 
 
         // Use shader model 3.0 target, to get nicer looking lighting
         #pragma target 3.0
 
         sampler3D _MainTex;
 
         struct Input {
             float2 uv_MainTex;
         };
 
         half _Depth;
 
         void surf (Input IN, inout SurfaceOutputStandard o) {
             // Albedo comes from a texture tinted by color
             float3 uvw = float3(IN.uv_MainTex.x, IN.uv_MainTex.y, _Depth);
             fixed4 c = tex3D (_MainTex, uvw);
             o.Albedo = c.rgb;
             o.Alpha = c.a;
         }
         ENDCG
     }
     FallBack "Standard"
 }