That's why I said a good quality velcro. I've never had an issue. I have moved or removed the velcro for one reason or another and have had to pry it off. I feel confident that a good quality velcro is a much better choice than hot glue.
I use this method in both a GTP and BRB cage with no issues. Both have pulled the unit off the wall several times and neither strip of velcro shows any sign of failing. Both of those have much more humidity than a ball.