Hi. I came on this forum for something else but I noticed your post regarding the melted housing box. I have a 16 suburban but with the same exact issue - i don't have the blind spot sensor but it is the connecting box to the rear parking sensors. I have no idea how it was affixed to begin with...I think it was just dangling there underneath the plastic, and finally I had a look one day and the thing had pretty much been melted to smithereens...so yeah, I've had the same problem.
I can't even tell how it was held in in the first place - there is nothing to attach it to.I've tried looking this part up online but can't find it anywhere. All it does is control the parking sensor, which I don't really need anyway and I'm sure not shelling out to get that fixed...