I drilled some small holes in the bulkehead that connects the 2 static ports togethers. I used small tie-wraps there.
On the longerons, I used Van's advice to make little curled aluminum clips, and affixing them to the longeron with an existing hole for a side panel rivet (don't have a photo handy). "Curl" may not be the correct descriptor, but basically the aluminum clip closes on itself to hold a cylindrical object. Basically, every few inches or so rivets that hold the longeron in place, I will have used a slightly longer rivet, and riveted the clip to the longeron. The curl is almost closed, allowing you to insert the tubing in it, and pinching (the aluminum) closed. Works well, little weight, no extra holes.