Is 1000ml of 'hot-ice' solution dangerous?
The heat generated increases directly with the amount of sodium acetate trihydrate used, but the maximum temperature, ignoring surface effects, should not change at all. After all, if the heat in 300 ml is used to raise the temperature of 300 ml of substance, or if 300 kg is used to raise the temperature of 300 kg, it's being spread out proportionately. No matter how much you use, it won't exceed ~58 C

However, do not try this in a container that would not allow room for expansion, e.g. a glass bottle, as in crystallizing, sodium acetate trihydrate might take up more room. See warning at http://chemmovies.unl.edu/chemistry/dochem/DoChem058.html. You could safely do this on a polyethylene cutting board, though, which melts at ~100 C