Honestly I haven't seen a heater get so hot that it'll cause any issues as long as it's submerged in water it'll be good. Not perfect practice to have a heater touch anything as it'll create a hotspot but like I said a heater in water will never get hot enough to melt anything.
Thanks everybody I had my doubts as well I'm just going to install it vertically to be safe I'll have another one in the first chamber under a floss holder thats going to be the primary anyways so this is just the backup