This pairing has recently become my new obsession and I'm constantly on the lookout for good Samifer fics close to your description. Unfortunately it is not so easy so if you have any recs I would be grateful, too!

My favorite ones so far:

Fear of Falling by Hallucifer
https://www.fanfiction.net/s/9936627/1/Fear-of-Falling (https://www.fanfiction.net/s/9936627/1/Fear-of-Falling)

Summary:
Cage!fic. In possibly the worst place in creation, with only a bitter and angry Michael still wearing Adam for company, Sam decides sticking with Lucifer is better than nothing. But with memories of what he learnt about Lucifer while his vessel in mind, Sam finds that maybe the devil's companionship is not as bad as it seems. Eventual Samifer.


I cannot even begin to tell you how awesome and touching this story is. I was actually somewhat depressed and fell in bit of a reading slump when I finished because it seemed like no other fic would ever compare and hit me like that.


Loved You First by Hallucifer
https://www.fanfiction.net/s/9697222/1/Loved-You-First (https://www.fanfiction.net/s/9697222/1/Loved-You-First)

Summary: Lucifer wanted so much for Sam to understand. If he'd just been able to explain, to give his side of the argument. If he could have just let Sam know how much he truly cared for him. Lucifer addresses his thoughts to Sam on everything he truly wanted to say.


Every Heartbeat by suchanadorer
http://archiveofourown.org/works/625133 (http://archiveofourown.org/works/625133)

Summary: From his cage, Lucifer can only see glimpses of Sam's life.


Learn to Fly by devilsduplicity
http://pickthelock.livejournal.com/6304.html (http://pickthelock.livejournal.com/6304.html)

Summary: Lucifer holds Sam hostage at a strange hotel. It's not as bad as Sam thinks.


And I'm sure you have already read

- The Fourth Wall series by entangled_now
http://destielebooks.tumblr.com/post/54342797374/the-fourth-wall (http://destielebooks.tumblr.com/post/54342797374/the-fourth-wall)

and

- The Conversion series by trollmela
http://archiveofourown.org/series/28462 (http://archiveofourown.org/series/28462)

or with PDF files with art here:
http://trollmela.livejournal.com/5975.html (http://trollmela.livejournal.com/5975.html)

I have combined the PDF's with art into one single PDF file for myself if you would like to have it.


Lastly, I would like to rec a very fun, lighthearted cagefic that is not Samifer but simply Sam, Lucifer, Michael, Adam making the most out of their time together and actually enjoying themselves (not like that, it's gen ;-) )

Sam's Hell by Ella M. Nite
https://www.fanfiction.net/s/6629158/1/Sam-s-Hell (https://www.fanfiction.net/s/6629158/1/Sam-s-Hell)

Summary: For a hundred-and-eighty years Sam's soul has been down in the cage with Lucifer, Michael and Adam. Thank goodness for the rules ... otherwise Sam thinks he might have been in agony the entire time.


I hope you enjoy and have found a few fics you haven't read yet!