Put heat pads on the side of the tank, and not underneath.
Putting them underneath the tank is a sure fire way to eventually end up cooking a spider or 5.
Get a panel heater for the room otherwise. Not very expensive for the heater and much cheaper electricity wise as well. I use this for my spiders that Im trying to breed and keeps their tanks above 30 degrees if put close enough to the heater.

Problem is, i've build my "setup" on a wall, like big wall unit built into the wall and the room is rather large. So to use a wall heater will end up costing more because its going to need to completely warm the entire room up.

So i should put the heating pads on the sides of the tanks, not the top? Can i use 1 heating pad for two tanks if they next to one another? Considering the heating pad is silver one side and white the other like the cheap ones at the pet shop.

I'm not an experienced keeper, but I did experiment with the heating of the tank of my B. Albopilosum quite alot when I got it. I have found that if you heat the tank from the bottom it tended to dig alot of holes al over the tank, even if I just heated half the tank. I then put the heating pad on top and it dug one hole and made that its burrow.

My brother also has a B.Albopilosum of the same age, from the same breeder and his only gets heated at night with a room heater and it seems fine as well.

IMO the heating of the T's tank is not cast in stone and you should experiment and see what works for the type of tank(ea material it made of) you use and what type of T it is. Its always a great idea to use thermometers in the tanks to see to what temp. you heat the tank and to try and find out what the weather is like where the T comes from.

Well i'm going to try and put the heating pad on top of the enclosure tonight and see how it goes. If all goes well, I will move the heating pads to the top of the enclosures and then just mount one on the well and have all my slings lean up against it, except my Arboreal ones, they can be heated from the bottom if i'm not mistaken.

Try it tonight and see how it goes. I'm not sure about the Arboreals. I'm only getting my first ones soon, if all goes well.

Garfield wrote: I'm only getting my first ones soon, if all goes well.

All is going well.
I have my eye on your little one, Matilda. Busy moulting into first instar.

@splurge. I heat my arboreals on the side as well. Lots of them, especially as slings, burrow or stay low to the ground when they are young.