From what I was able to find, the interior dimensions of your 2012 Sprinter are 72" x 70". You could use a cargo net like the Gladiator # GC94FR which is 6' 9" x 8'. There will be a little extra but nothing overly excessive. It comes with 4 ratchet straps but you could add some like the # EM04418 for added security. The ratchet straps will make it easily removable when not in use.
Then you would need to mount your D-rings like the # 3486554 or # 337B46 if you don't already have them.... view full answer...