To get the bathroom nice and toasty, I have a shower before Theron's bath, either with Daddy holding him in the bathroom, or with him lying on his changing mat while I sing at the top of my voice through the [clear] shower curtain. He gets so excited everytime he hears the shower now, as he thinks that bathtime is next!
Doesn't help when Daddy showers at 3am to get ready for work
It did take him a while to get used to the bath experience too.