Inner tubes are better for the clamping force, you aren't using enough clamps, really if you carry on using clamps you should use a pressure strip or have them max 2 inches apart. The tubes gives very even clamping pressure.
The holes at the tips are a good idea when using boo but the rest of the lams should be full width then all you need to do is tape them all to the form to stop any movement as you clamp.