Only had 1 boa- large BCI (other than temp. rescues) & she loved to 'bask' on top of her very sturdy home-made extra large hide- rectangular & flat (made of water-
sealed wood & tile board top) with washable non-slip carpet on top. The height put her closer to overhead warmth as UTH below the hide warmed from underneath.
She enjoyed both being IN the hide, & on top of it as needed. It was very EASY to make, also...& not expensive, & a pair of doorways side by side at one end made
it much easier for her big body to come & go. I've not seen other hides made that way, it was my own inspiration that appeared to be well-appreciated as she often
cruised her cage, & would pass herself coming & going in/out of her hide, but it was very long ("deep") so she felt secure at the far end as well.