I assume you are making the controls public by editing the Designer.cs file, there is a reason they put the warning in there that your changes will be lost.
The correct way is to mark the control's Modifers setting to public in design view from the properties menu for your control.

EDIT: Well I'll be damned, you don't have a modifiers option. Well, here is a workaround, create a property that is public that you control that can point at the private member.
public RadPageView pgvTabsPublic
{
get {return pgvTabs;}
}
Using this you can have other classes call yourForm.pgvTabsPublic and it will point them to the internal private pgvTabs member.