Questions for Heating A Plastic Tub

[dr del]

I've looked at other posts but I have specific questions. I got two plastic tubs (a sterilite and a hefty) to move my ball python and my red tail boa into. And I'm currently looking to buy heat tape for them. So here are my questions and I apologize if they are dumb but I'm a paranoid snake parent and want to make sure everything is perfect and safe.

1.) When setting up heat tape, can you attach it directly to the plastic tub or does the heat tape have to be attached to the surface the tub is resting on? In every installation video I've watched they've all had the tape attached to the surface the tub is on and not the actual tub itself.

I usually attatch it to the surface it is sitting on - this lets you remove the tub without having to worry about thermostat probe movement or restricting how far you can take the tub.

2.) This question is a follow up of the first one (if the answer was yes the heat tape can be attached to the tubs directly). This is difficult to explain but I'll try my best.
If you flip a tub over to look at the bottom, tubs usually are raised around the perimeter of the tub while the middle is somewhat of a dip. On one of my tubs the center area (before the raised perimeter) is 10" wide with an overall width of 14" and the other one is barely 12" wide before the raise with an overall width of around 15". Because heat tape isn't found in 10" width, would it be ok to get 12" tape and have it attached to the raised perimeter with the gap between the tape and the dipped middle part of the tub? Or should I get the 6" heat tape?
And with the second tub (the one that's barely 12" before it hits the raised perimeter), if I get the 12" wide heat tape, the ends will be slightly curved outward where the perimeter of the tub starts to raise and I just wanted to make sure if that was safe. Or if the heat tape has to be totally flat and not curve at all?

That's why we "dial in" the temps on the thermostat to get the correct temps in the enclosure itself.

3.) One more follow up question to the first one: When attaching the heat tape to the tub, should I use double sided tape or just attach the heat tape directly with aluminum tape?

Thanks in advance and again I'm sorry if it's a bit confusing. I don't know how to explain it any better haha.

When attatching to the surface I usually use aluminium tape just for the resiliance.