my house is heated by window ac's so my house is always at diff temps. Btw 64 in mornin to up to 80 in afternoon. I have very little control over this.
Never use a uth without a t-stat and you answered your own question as to whether a dimmer switch will work, it won't.
If your room temperature goes up and down like that so will your uth, you will need a thermostat.

Truthfully ten gal tanks work "ok" under the best of situations, you might look into getting a t-stat and housing your snake in a tub on heat tape.