Use some of that FastEddy servo tape. I once used a 1" square piece to mount one of my receivers and once set it would not budge when I tried to remove it. I actually tore the receiver case in half trying to get it off LMAO. I ended-up prying it off with a screw driver.
The tape in combination with some sort of strap on top squeezing it down to the chassis should do it.
My servo in my mini-t is mounted in this manner. It does not budge.
The tape in combination with some sort of strap on top squeezing it down to the chassis should do it.
My servo in my mini-t is mounted in this manner. It does not budge.