All sounds fine. don't change a thing. Just keep in mind if the air temp is too cold, larger snakes have trouble raising their core temp and in an effort to do so, can burn themselves on surfaces that are too hot such as undertank heaters.

Try adding lots of fake plants for cover. He might feel safer and not burrow so much.

I use seedling heat mats myself. They're larger, cheaper, and don't get as hot, but hot enough.

HydroFarm MT10006 - 17W Seedling Heat Mat - 9x19.5 in.