You can put the soaking tub in the sun, on a heating pad, under a heat lamp, in the enclosure, in a heated room, you can continuously trickle warm water in, or replace the water every few minutes, etc… I sometimes use a five gallon bucket to catch all the cold water while waiting for the hot/warm water to arrive at the tap. Then I can let the hot water warm up the cold water to the correct temp. This usually results in 2 or 3 gallons of warm water. I can fill the soaking tub several times from this bucket of warm water. I dump the cooling water and just refill with warm water from the bucket. This keeps the water clean, fresh and warm. Then I use the excess leftover water to water all my plants outside.
Whatever method you use, watch that temp closely. Soaks are very good for them. Sitting in cold water isn't.
