How to change or permanently set background image(wallpaper) in openbox WM?

Hey I just installed Arch Linux in Virtualbox btw with **openbox**, **gdm** and **rofi**. I wanted to **set a wallpaper** for the ***background***. So, I added this line in the end of my **/home/user/.bashrc** file -

feh --bg-fill ~/wallpapers/squid-girl.png

The problem is that it doesn't set the wallpaper just after I successfully login in an openbox-session but after I open an terminal window in an openbox-session. So, that is the matter. Now how am I supposed to/should set it?