Sorry for using this link:
That is my most favorite background that I have done. I decided to approach out through digital painting and looked up YouTube tutorials. Don't underestimate YouTube tutorials.
This is the tutorial I followed:
Another great tutorial for backgrounds (especially interiors) is this one:
That one will help you get perspective right where there are geometric shapes and help you keep your location consistent.
I agree with the OP, though. It's often a good idea to do a background one in a while to establish spacing - where each character stands in relation to each other. The drawback of backgrounds, though, is that if they're too detailed, they distract from what a reader is supposed to focus on. That's why the idea of sometimes having no background works.
It's not a chest. It's a legitimate story telling strategy.