I'd recommend watching the how to video on this link at Big Apple Herp - it helped me get a basic idea when I first started.

http://www.bigappleherp.com/Flex-Watt-Heat-Tape

I can't answer on how to secure the flexwatt to the cage, as all my racks and cages come with the flexwatt pre-installed.

As for how / where to place your thermostat probe:  You should NOT place it between the flexwatt and the cage.  However you end up securing the heat tape to the underside of the tank, you will want it to be smooth and completely flush with the cage belly.  You won't want the probe creating a buldge between the tape and the cage.  After you get the heat tape secured to the underside of the cage, you will want to secure the probe to the bottom of the flexwatt with electrical tape.  You want your probe in direct contact with the flexwatt.

Setting your thermostat is more or less a trial and error thing.  The thicker your layer of substrate, the more dropoff there's going to be between your thermostat setting and the actual cage floor temp.  I use an infrared temp gun to check the temp of my hot spots and then adjust my thermostats until I've got the hotspot I want. 

bka mama:  thank you, I did watch that.

KCB:  Thank you for your response.  I did exactly what you said not to do.  I put the probe between the cage and flex watt.  The instructions are not very clear.  You are right, there is a lump.  I will correct it.  I did secure it to the bottom with duct tape, cutting thin strips by splitting the roll.  I will put the probe on the bottom of the flex watt and have the heating element flat against the cage.  I thought that would make more sense, but wasn't sure if I could get a reading from the bottom of the flex watt.

Thank you for your replies!

IMO, the flexwatt should be secured to the outside bottom of the cage using metallic tape found in the insulation section of your local hardware store.  The probe should be secured to the INSIDE of the cage using cable clamps (not tape).

Question - what cage are you using?  Specifically, what material is it and how thick is it?

+1 to bsharrah.  You're going to want to control the temperature of what the snake is actually coming into contact with.  Putting the probe on the flexwatt itself will allow you to control how hot the flexwatt itself gets, but the temperature of the inside of the cage will be dependent on what material the cage is made of, and what thickness it is.  Much easier to secure the probe on the inside floor of the cage, right over where the flexwatt is.  I use those 3M stick-on cable clips, and they work pretty well.

Also wanted to point out: those strip thermometers are worthless.  They will tell you the temperature of whatever they are stuck to (aka the wall of your cage), not the ambient air temperature.  I would recommend getting a digital temperature and humidity gauge (because the analog humidity gauges are also pretty much worthless, and it sounds like you might have one of those, too).

Probe directly on the flexwatt.  Here's a link to a forum with that same question, and numerous answers, including an answer from Jeff Ronne, aka The Boaphile (of Boaphile Enterprises) (all saying probe directly on heat tape).  I've also had personal conversations about flexwatt use with both Brian Barczyk of BHB Enterprises, and Jeff Johnson over at Freedom Breeder, who both also say the best place for a theromstat probe is directly on the heat tape.

Thanks again.  I did place it on the outside of the flexwatt.  The cage is like a boaphile style and material.

Again, thanks to all that replied.  I've been out of the hobby for about 15 years and so much has changed.  You knowledge with the times, and sharing that knowledge, is much appreciated.

Some of my thermostats have a max setting of 96 degrees.  If I placed the probe on the heat mats themselves, how would I acheive a hot spot of 90 degrees through 1/4"-1/2" of plastic with a 96 degree heat mat?  (not asking to be snarky, I'm geniunely curious)

Another reason I put the probe inside the cages is because there is only a 1/4" gap between the stacks.  Some of the thermostat probes are almost 1/2" in diameter.  Someday I will have all Herpstats with their sleek little probes, but for now I've still got to work with some fatties.

Well, okay...if your thermostat tops out that low then you'd obviously have no choice.  I've only ever used ranco and herpstat thermostats...so I've never encountered that problem.

As for the gap issue...I have a ranco thermostat (1/4 inch probe) running my stack of boaphile cages (zero space between cages in the stack), and we just placed the cage (with the probe taped to the bottom) on top of another cage.  The probe has the weight of the whole stack of cages, all the substrate, and the animals pressing on it, and it functions just fine.  In fact, because it's squeezed by the cages it's between, there's no chance of it coming detached from the heat tape.

that was my concern, if I have the thermostat set at 88, then the actual ground surface is probably only 83 after the material and substrate.  I was advised to get an infrared heat gun.  My probe is about 1/4 to.  I have the cage on a table top type surface on an old computer armoire.  I was wondering if the temperature of the flexwatt against the wood surface could be damaging or a hazard.  So, I took those little rubber sticky nubs and used them as feet to prop it up a little.  now my rock pushes the bottom down since there is a gap.  if you are stacking your cages and the flex watt is on surface to surface, should I just take those nubs off and just let it rest against the wood top??  I think I read that there should be a little space for ventilation, but how can that be with the boaphile cages when they are flat on flat?

advice, take them off and let it ride..?

The flexwatt could definitely be damaging to the wood surface, and could potentially be a hazard.  You definitely want space for ventilation, so I'd keep the nubs.  Even with those, I'd check periodically to see if the wood is getting discolored.  You might need more space.  Before I had the stack and had cages on tables, I went so far as to set a cage on a couple of two by fours - not the most attractive option, but effective.

If you want to secure the probe to the flexwatt, like bsharrah said, use aluminum tape.  The infrared heat gun is a fantastic idea.  Get your temps dialed in just right before you introduce the snake to the cage.  A floor temp of 83 seems pretty low...what species are you housing?

sorry, I mistyped.  it is not a wooden cage, but like a boaphile.  I plan to get a heat gun by this weekend.  I am housing a pastel ball.

Correction, the cage is not wood.  I do have it on a wooden surface.  I kept the nubs on, but I am thinking that if the flex watt is at, say 89 degrees, it would be the same as the greenhouse effect with the sun shining in directly on the wooden surface.  Then again, with electricity and the electrical current, should the wire touch the surface, that could be trouble.  However, I have the connectors wrapped with a great deal of electrical tape.  I'm now concerned with that.. knock on wood.

foil tape will work the best can buy in home depot or ace hardware

lay your probe right on top of the flex watt tape and connect to temperature controller.zilla makes a very good 1000 watt controller otherwise your heat tape will get very hot.zilla has it's own probe just lay on top of flex watt and use foil tape to secure it.and that will regulate your temp fine GOOD LUCK

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