I have decided to secure the interstage coupler to the forward booster airframe tube with an anchor bulkhead. Pic 1 shows the booster av-bay bulkhead and the anchor bulkhead. Pic 2 shows how the two bulkheads engage. The anchor bulkhead will be epoxied in place within the forward airframe tube on the booster (as shown in Pic 3) and the three all-thread rods from the interstage coupler will stick through the anchor bulkhead and be secured with wing nuts...