I have 2x 60gal Zoomed UTH's as side heat pn my PVC enclosures. But my snake room is also heated to 75-80 degree ambient so it keeps it perfect. But I used to have them in my living room and the ambient temps would drop to 60 degrees, even with the two heating pads. It's very hard to keep an enclosure that size heated properly if you don't have the room heated.

PVC is also not a very conductive material. My UTH's are set to 100+ just to hit a 89 degree hot spot.