In the interest of accuracy and not misleading anyone who might be tempted to follow.
Magnets.
I have today decided to abandon using magnets to close two ends of the panels (at the doors).
I tried to use 4mm X 0.5mm disc magnets.
Unless the opposite polarity strips had the magnets very, very, close to the same centres the pull was poor.
Using a 6inch steel rule (as a test piece) on either polarity strip, the pull was decent but a steel strip has too much damage potential AND even with 0.5mm thick magnets the faces did not lie flat.
New Route.
I am going back to Velcro for the panel "door closers".
It is the only easy obvious way to get two ends fixed together with no midgie tunnels.
I will however modify the end 80mm ish of the meeting panels to "solid" material thus removing the immediate potential for the Velcro dragging at mesh.
Onward and em, forward, I hope.