Consuming ASP.NET Web API REST Service in ASP.NET MVC using HttpClient

I have an ASP.NET MVC application from which I would like to consume an ASP.NET Web API REST service. So I have found a piece of code here.

In my case I would like to call ASP.NET Web API method (DumpIntoFile) from a method in a class in my ASP.NET MVC app (this class is not a controller). I need the execution not to continue until call to DumpIntoFile is completed and finished. How can I do it? I have never used async and await so I do not understand at all how they work.

    public void GetData()
    {
         Warehouse myData = new Warehouse();
         myData.id = 1111;
         myData.name = blabla;

         string path = "c:\temp";
         string filename = "myData.dat";

         // Stuff here
         this.DumpWarehouseDataIntoFile(myData, path, filename);
         // Some other stuff here
    }

    public async void DumpWarehouseDataIntoFile(Warehouse myData, string path, string filename)  // See Warehouse class later in this post
    { 
        //Hosted web API REST Service base url  
        string Baseurl = "http://XXX.XXX.XX.X:YYYY/";  

        using (var client = new HttpClient())  
        {  
            //Passing service base url  
            client.BaseAddress = new Uri(Baseurl);  

            client.DefaultRequestHeaders.Clear();  
            //Define request data format  
            client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));  
              
            // Serialize parameter to pass to the asp web api rest service
            string jsonParam = Newtonsoft.JsonConvert.SerializeObject(myData);

            //Sending request to find web api REST service resource  using HttpClient

            // How can I pass parameters jsonParam, path and filename to below call??????? Concatenating it?
            HttpResponseMessage Res = await client.GetAsync("api/Warehouse/DumpIntoFile");  

            //Checking the response is successful or not which is sent using HttpClient  
            if (Res.IsSuccessStatusCode)  
            {  
               // Some other sftuff here
            }
         }
    }

The Warehouse object is as below:

public class Warehouse {
    public Warehouse();

    public int id { get; set; }
    public string name { get; set; }
    
    // some other stuff here
}

And web api rest controller with method:

public class MyWebApiController : ApiController
{
    public bool DumpIntoFile(string data, string path, string filename)
    {
        bool result;

        Warehouse myData = JsonConvert.DeserializeObject<Warehouse>(data);
        string myPath = path;
        string myFilename = filename;

        // Here rest of code

        return result;
    }
}

Also I am trying to do below:

1. Avoid to hard-code the URL because if the ASP.NET Web API REST service is published in another server in a future, then I need to touch code, change it and publish again my ASP.NET MVC application. Maybe putting a the url in the web.config file and read from there?
2. How can I pass the parameters jsonParam, path and filename to the web api rest service? concatenating it?

NOTES: I am using NET 4.5 and Visual Studio 2013.