Daraxir

I dont know where to hide guidance unit/battery/reaction wheel module/advanced inline stabilizer. They are too big for service bay so I want to hide them but i dont know how. There are some structural tubes but its empty tube and I cant put anything inside. I need to shield this part with something similar to protective shell used on a top of the second stage(cargo):

This was the biggest decoupler available I will use structs then.

Hello, I'm building 2 stage rocket similar to Falcon 9 with reusable first stage, but as I use decoupler showed on image, as I launch a rocket, second stage is wobbly and it immediately snap from first stage. What is wrong with it. I've built multiple 2 stage rockets before but it happened to me for a first time today. Under decoupler is Remote Guidance Unit to control that first stage at the reentry and Advanced Reaction Wheel Module. Thanks for some advice.