Spray the slow cooker with non-stick spray and heat on high while you're prepping the ingredients. Make a ball out of foil and place in the center of your slow cooker.
Combine sugar and ground cinnamon in a small bowl.
Open and unroll both cans of the crescent rolls and sprinkle a thin layer of cinnamon sugar over the dough. Roll dough starting on the long side. Pinch edges and ends to seal.
Using a serrated knife, cut dough into 1-inch slices. Place half the dough (or one can) in the slow cooker evenly. Pour half the butter and sprinkle half of the remaining sugar over the dough.
Layer the remaining dough in the slow cooker and pour the remaining butter and sugar mixture on top of the dough.
Place a sheet of paper towel over the top of the slow cooker, then place the top on. Make sure the paper doesn't touch the dough. Turn the slow cooker to low and cook for 90 minutes. Depending on your slow cooker it may take from 75 minutes to 2 hours. Start checking the rolls at 1 ½ hour. You may need to rotate some of them from the edge to the center using tongs or a fork if they start getting too dark around the edge.
You can dip them out of the slow cooker to serve or dump them onto a serving tray and serve them upside down.
If you want to put a glaze on them. Whisk together the powdered sugar, heavy cream, and vanilla until it's smooth. Drizzle over the rolls. You can double the glaze if you want more.
When removing the lid, do not let the condensation drip back into the slow cooker.
When the rolls are done, remove all of them from the slow cooker. Once they begin to cool, they'll stick.