Heating shouldn't be a problem. the usual 25w heater with an adjustable knob. fits well in a 1 gallon, be it a bowl or a tank. I have heated half gallons with 25w adjustable heaters, so it really isn't a problem.
Always test your heaters first with a reliable thermometer.
That's good to know. I thought 25w would be too much for 1 gallon but that's why I love this forum. I learn something new all the time.
Animal testing is a terrible idea; they get all nervous and give the wrong answers.