Before installing the enterior panels I had to install the foam strip on the underside of the rails. Instead of the original white foam strip, I bought a black version.
The white foam was looking very dirty because of greas from the rails, I think black is a better choice here.
I bought 8 meter closed cell sticky back foam strip in 20 x 3 mm. I ordered it at a (dutch) boat (nautical) parts webshop:
8 meter is way too much, but this stuff is handy for other things too.
Then I installed the interior panels, and I also placed some foam on the parts where the interior panels overlap. This will prevent wear when the two panels rub against each other, and it will prevent squeaking noises.