Here is the reason I want to add stall strip. First I have this beautiful Chipmunk plane from CMP which is not designed well and it tip stall even under normal landing (I hear that at least from 5 people who owned this plane). So one tip stall means my plane is gone, so why not tame that wing and add some stall strips.

To answer your question as why I want to stall the plane sooner is
I rather stall the plane at the root while the tips are still flying
So as you know, if the stall begins out at the wingtips, we'll see a wing drop (often violently and no way to control that during landing). But if the stall begins at the wing root, all we get is a nose drop, with the plane still under some control.
Adding stall strips will cause the plane to stall at root instead of tips on this particular bad design plane.
So my question to those who are expert is where I should add the stall strip, and how long should be the stall strip.
Thanks
Borna