How To Send 4 Double Values To A Webservice

I need to send 4 double values to a webservice. Which is the best way to send. Array or Arraylist. I read some where that Arraylist has issues to serialize.I am using the following code on the client .aspx page to construct the arraylist.

Code:

ArrayList CapPlan = new ArrayList();
CapPlan .Add(Convert.ToDouble(TextBox1.Text));
CapPlan .Add(Convert.ToDouble(TextBox2.Text));
CapPlan .Add(Convert.ToDouble(TextBox3.Text));
CapPlan .Add(Convert.ToDouble(TextBox4.Text));
After this arraylist CapPlan is constructed, what would be the syntax to send this arraylist to a webmethod?
DataSet dataSetCapitalPlan = clientProxyobject.CapStock(CapPlan.ToArray(double));

And on the webservice side how can I receive this arraylist that was sent?
[WebMethod]
public DataSet CapStock(string As_of_Date, Array CapPlan)
{
}