I’m heating my 4x4x2 box using an RHP and I was worried it wouldn’t be enough but it’s working great. I probably need a bunch more water tubs. I’m in a dry desert climate.I put water in tubs on shelves. This is one of my star boxes. I couldn't find a good pic of a sulcata box. I do NOT use heat lamps, Pond Shield, or substrate with the sulcata or leopard boxes. I only do these things in boxes meant to house little tortoises that need to stay over 80% humidity, you know, like Burmese stars.
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If your box is not sealed, insulated, or weather stripped enough, the heat will run more and dry everything out more. My heaters seldom turn on. Only two or three times a night usually. I have no problem maintaining 60-70% humidity with the water tubs.
@Nemytort How are you heating your box?
I don't. I had the bottom of a leopard box rot out after about 10 years, because those girls constantly peed and made a mess in there. I just dried it all out and put a plywood patch over the affected area. 10 more years now.
I had some wood rot in the star box shown above too because I did a poor job of working with the Pond Shield and there were gaps in the coverage. I like that stuff, but it is NOT easy to work with and you need a lot of it for waterproof coverage. Subsequent boxes turned out much better and have not rotted at all because I used the product correctly on them.
But to answer the above question: No mold ever in any of my boxes, treated or untreated.
The heat stays great on my WiFi thermometer, but I haven’t finished weather stripping yet. It might be turning on a lot.