I agree. UTH's or flexwatt is the way to go. I would hate to think about trying to heat a tub with a lamp... messy.
Definitely set the tub up a week or so before you get the snake so you can work with stabilizing the temps and humidity. Also make sure you have a way to keep the lid secure. I prefer luggage straps because they have a cleaner look, but you can also use bungee cords or binder clips...