Our backgrounds are 3D, they are not flat on the back and so there is plenty of room behind the background to install heater and run filter pipes. It’s important to install the filter inlet pipe end in front of the background close to the bottom, so all the debris is sucked in. You can run the pipe behind the background and under the gravel/sand, so only the tip of inlet pipe is visible.
The outlet pipe should be located somewhere at the top of the background in the corner. If you install heater behind the background and you have a large aquarium it’s good to install additional power head or small internal filter next to the heater, so the warm water is pushed out from behind. This way your aquarium water temperature should be the same in whole aquarium. See pictures how to hide aquarium filter pipes here