Greetings,
I would install it enough off the floor to not have to worry about water on the floor touching it. Have you calculated the number of BTU that you need? Many heaters will run off of 120V at 1/2 the BTU output if you wanted to GFCI protect the unit more cheaply. I have several electric heaters in my bathrooms and none are GFCI protected which is of course the cheapest option of all.
Hope this helps, William