Heating a room with resistors (designing a heater)

If your doing the floor heat method I would recommend using pex pipe with a heating tape inside it.
Cat pee corrodes any metals eventually and some cats regardless of age love to chew on wires too!
Just using a standard baseboard heat line voltage thermostat would be good enough to control it as well.

If you feel the need to heat your doghouse, then your doghouse is probably too big for your dog!

But if you persist, then please incorporate a thermostat to close the loop around the temperature, as some nights will be a lot warmer than others.

If you move the Kenel near the house you can feed it with a fan from air ducting to the house in a small loop, won't have to heat anything. You can't just place a static heater in kenel and expect it to keep the temperature stable because it's completely dependent on the ambient air temperature and flow. Putting enough heat capacity in there to keep them warm on the coldest windy winter days will kill them on the sunny windless ones. As Dick said you'll need some kind of temperature monitor.