Put the probe over the heat source and the unit itself on the cool side. That way the probe which is called outside on the accurite will tell you how hot your UTH is and the unit(says inside) will measure what the temp on the cool side.

I tape my probe to the tub with blue low stick painters tape. There are no fumes and the stuff comes of easily so it could never do any damage to your snake like regular tape could. I have 50+ snakes and have been doing this for many years without any problems whatsoever. I am a contractor and have been using this tape for years it wont even pull the hair off your arm. It really only adheres to smooth surfaces and once removed will barely stick to anything else again.

BP's dont need light, just whatever ambient room daylight.

A thermostat is a must! or you will never have correct temps and could even burn your snake. The tub you have is for a full grown snake. I dont know what size yours is but that is also something to consider. It is also best to have a small gap(as mentioned earlier) inbetween the bottom of the tub and the table top it is resting on so the UTH can breath a little and not heat itself up too much.

Hope this was helpful