How deep is your substrate?
what size UTH do you have?
average temps in the room you keep your snake?
These will all effect the temp from the UTH to the inside of the tank, too deep of substrate makes it harder for heat to get through it, small UTH with a low room temp will effect the temp as well. UTH were made as a secondary heat source to use in conjunction with a bulb, they work well in racks because they are surrounded by the wood. if your room temp is in the 70's you'll be lucky to get a 90 degree hotspot with any kind of substrate. That being said, I would still recommend getting a rheostat/dimmer or thermostat with a probe as a precaution in case there is a short that causes a fire or for some reason your house gets into the high 80's and 90's.
you can get a sterilite-like tub with a lid from any store that sells them, drill a couple holes on the sides from the inside out(to keep the rough edges on the outside of the tub), add substrate and hides along with the UTH and thermostat on one side of the tub. place it on a solid surface(wood, metal, tile) you can buy some rubber stoppers to elevate the tub a bit. Thermometer with a probe or temp gun and a digital hygrometer to monitor the temp and humidity. You do not need a "day" light so you can save some electricity and run a red bulb or ceramic bulb all day, the room gets enough light on it's own, the daylight is for your viewing pleasure.
you can also get a piece of Plexiglas from your hardware store(some will cut it for you) drill a couple holes and add some drawer handles on top and use this to cover your screen top. You didn't mention the size of you snake but I would personally get a larger tank.