Help with Nerf Recon!!!!?

Like a lot of people's guns, the back of the plunger tube game off after modding. What is the best way to fix this? I don't want to spend over 7-10 dollars if possible. Please leave a DETAILED description on how to fix this (list materials, steps, etc....). Also state if this method needs further padding and if so, what type of padding to use and how much will do the job. PLEASE DON'T ANSWER THIS QUESTION UNLESS THIS HAS HAPPENED TO YOU AND YOU KNOW IT WORKS AND WILL LAST FOR A WHILE!!!!