Model Binding binding at more than one level - asp.net

Question

I have several forms, all which require a checkbox for each province/state. Therefore, I've made a partial view to render the checkboxes inside a form to promote code re-use. But when the user submits the form to a controller method, the RegionsViewModel does not get binded. The overall question is, how can I get multiple forms to share a partial view and view model?
Here's a sample code of my situation
Models
public class Form1ViewModel
{
/* Some properties */
public RegionsViewModel Regions {set; get;}
}
public class Form2ViewModel
{
/* Some properties */
public RegionsViewModel Regions {set; get;}
}
public class Form3ViewModel
{
/* Some properties */
public RegionsViewModel Regions {set; get;}
}
public class RegionsViewModel
{
public bool ON {set; get;}
public bool QC {set; get;}
/* this continues for all provinces and states */
}
Controller
[HttpPost]
public ActionResult Form(Form1VewModel model) {
//All properties except for model.RegionViewModel does not bind properly to the submitted form :(
}
Form1ViewModel.aspx
<% using (Html.BeginForm())
{%>
<!-- Binds some property -->
<% Html.RenderPartial("Controls/RegionSelector", Model.Regions); %>
<input type="submit" value="Submit Form!" />
<%}%>
Controls/RegionSelector.ascx
<%=Html.CheckBoxFor(x => x.AvailableProvince_ON> ON
<%=Html.CheckBoxFor(x => x.AvailableProvince_QC> QC
<!-- Binds to all provinces and states -->
Update
Replaced "Model.RegionSelectorVm" with "Model.Region". Thanks for finding the bug in my demo code Darin Dimitrov.

Answer 1

What is RegionSelectorVm? It seems that this is the type of your partial. Try with editor templates. It's cleaner:
<% using (Html.BeginForm()) { %>
<!-- Binds some property -->
<%= Html.EditorFor(x => x.Regions) %>
<input type="submit" value="Submit Form!" />
<% } %>
and inside ~/Views/Shared/EditorTemplates/RegionsViewModel.ascx:
<%# Control
Language="C#"
Inherits="System.Web.Mvc.ViewUserControl<AppName.Models.RegionsViewModel>" %>
<%= Html.CheckBoxFor(x => x.ON) %> ON
<%= Html.CheckBoxFor(x => x.QC) %> QC
<!--
Continue with inputs for the provinces and states
which are part of the RegionsViewModel model
-->
Now everything should bind correctly.