I wouldnt worry too much about it being on the floor for short periods, these animals are built to be out of water, the real killer would be if its body slime dries out. I recently had a 6 foot green morray eel. He was fine in his tank for about 6 months and then one day decided the floor looked better than his tank. He must have been out of water for a long time because there was no water drops on the floor it was all dry. I went to grab him and he budged. I peeled him off the floor and popped him back in the tank and he was fine within an hour. As for your issue, make sure to cover all the open gaps in your lid and maybe weigh it down with a brick or bag of gravel. You may even want to consider dropping the water line an inch or 2
