I'd go for floor heat.
You haven't stated what material your enclosure is, you haven't even said which dimension the 45 is, or what your units are (I'm guessing cm), whether aesthetics are important to you or you just want it to be practical, whether cost is important, whether you plan to use this enclosure permanently or upgrade to something else, whether it's your only snake or you'll be housing it in conjunction with others... all of this makes it possible to give you advice and offer ideas which work for your circumstances. If you can't be bothered describing your needs, it's not possible to give you the best option for providing floor heat in this enclosure.
Best of luck.