I haven't tried it on my system case
yet, but a method I've used successfully on a hard aluminum camera case is to put a bead of silicone gasket stuff into the channel on one side, then lubricate the mating surface with a light oil or grease, let the silicone skin over a bit, then close the case until the silicone sets.
Make sure you're thorough with the oil, and you may want to test by only doing a short section at first.
After it is set you can trim any places where it may have squeezed out or whatever. Ideally you want the bead to be only large enough to just kiss the mating surface.
You end up with a resilient seal inset into the channel that is perfectly mated to the outer shell.
This is one of my projects for the spring, I'll try to remember to post my results.
If you want to do the tubing method, these guys have lots of choices;
www.usplastics.com
