I have not use anything like this before, so these are my theoretical musings!
You need to worry about how much room you have in front & behind the background. As Speed said, this setup is prob better used in a deeper tank (like a 75).
If you put both intake & output behind the background, you wouldn't have a lot of circulation between the front & back. <Or almost none in the the front.>
I am thinking of this setup as a sump (except that the sump is inside the tank). In that case, you would want your intake behind the background, and the output in front. < You can hide most of the output hose behind the background, but arrange it so the water is running into the front. > you would need to have an opening to allow water to move from the front to the back & from there to your filter. you can cut slots on top, or possibly some kind of underwater hole with a screen. The size of the opening is determined by your pump flow rate. A total area of 2-3 square inches for all your holes/slots should be enough. <4 happens to be the recommended slot area for my overflow at 750 gph
... the XP3 runs less than that, so you should be safe.> You can of course have more holes/slots than is needed ... in case some gets plugged up between cleaning.