I have a base form in another project that enforces the same look & feel to all our WinForms programs. I inherited from that BaseForm, to create my own template, BaseVie
This MSDN article gave me the answer.
"Not all controls support visual inheritance from a base form. The following controls do not support the scenario described in this walkthrough: WebBrowser, ToolStrip, ToolStripPanel, TableLayoutPanel, FlowLayoutPanel, DataGridView. These controls in the inherited form are always read-only regardless of the modifiers you use (private, protected, or public)."
I used a docked Panel and a SplitContainer instead of a TLP, and now I can drop anything I want into them.