Know it's late for this one; but when any electrical or mechanicals are involved; it pays to do a test run prior to making any permanent mods. For example; set all pumps and filters in future location; fill tank to planned depth; connect all humidifier and/or mister equipment and plumbing; set up the heating/cooling systems, test everything! Then check all works as planned and make adjustments if needed. This is the time to "measure 3 times and cut once."

Then, when tank's no leak water integrity (including any bulkheads) and all equipment checks OK; you take it all apart and start the artistic moulding of background, bottom, etc. Don't forget to make sure that all electrical equipment can be removed later for service or replacement if required. Hope this helps in the future and good luck !