I needed an extra bracket for an original gen 1 simplisafe door/window sensor and found the basic model from Conando on Thingiverse. Wanted to add the battery support, the 3M command strip slot, and a bit of reinforcement on the locking tabs. 

I printed it flat on the bed with tree supports under the tabs. Seems to work fine. Tabs may be the weak spot, but will work for my needs.