If this emulsion is thick at 40 deg C, then it indicates a very high percentage of gelatin. Normally, gelatin is coated between 5% and 10%. Any higher leads to difficulty melting as noted above. I'm afraid I cannot give much advice in this case as I try to stay at what I am comfortable with in terms of concentrations.
If the paper curls, you may be putting down too much emulsion at one time, you may have humid darkroom conditions or you may be using a cold press or soft textured or low weight paper. I use 100# paper, or higher, and I do not use cold pressed.
I wish you the best of luck.