Shelling (please advise)

I really need help for this.

I have uses GHX for several years , but not quite experience with Rhino editting.

I have tried several attempts to make this thing to have the thickness through GHX or Rhino. But cannot do it. 

What I want is to have the thickness of this model without gap or intersecting edge . Is there a way in rhino or GHX to do that efficiently? Or I have to manually edit the model after do the (OFFSETSRF) in Rhino. 

I attach the file.

Need it for my project dued really soon. 

Really thank you for anybody who can help me with this.