Might help to give info on the species. Sounds like it is not a BP from your post, but I'm not sure what it is.
I like the ultratherm heat mats (Reptile Basics sells them) or you could get heat tape that they wire for you from them as well which is just as easy to use as a heat mat. In my experience, the zoomed heat mats heat fairly unevenly. Not unusable, but annoying to find and test the hot spots of the mat to keep it all in a safe range.
If the species is small or good at escaping, I prefer these gasket tubs. Plenty of size for juvies of most species through a QT period and extremely secure. I'm sure you have a tub already since you state the size, but a consideration if it is a pretty small snake if the lid isn't extremely secure. I've had poor luck with adding binder clips or luggage straps to secure long sides of tubs with small snakes. There are various sizes in this style, but this is a good size for most things. https://www.target.com/p/sterilite-3...XDtUAaQWJgS6Bf
When working with tubs, I like to tape the UTH to the table (My QT table is just a particle board surface on a table we built at one point), then tape the thermostat probe to that on the cord right before the probe tip, then just set the tub over it. This lets me fully remove the tub for thorough washing without worry about probes or electrical.
It does end up with a slight air gap above the UTH below the tub, but that air gap is supposed to be good for UTH anyway, it gives space for the probe when you use tubs that have the feet like the gasket sterilite tubs I linked, and it doesn't need to be set much higher on the thermostat than when it is pressed against the bottom of a tub. 1-2 degrees is what I see for mine, though it may need more if there is a draft or A/C vent blowing along where the tub is placed. It also eliminates the odd bump that you usually get by sandwiching a probe and taping the heat mat to the enclosure itself.
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