pipe the supply water to the toilet with hot water. okok bad joke, you could move the toilet to colorado, we dont have that kind of humidity out here. i’ve seen the results of what your asking every time i go to mexico and have wondered myself how to handle that problem, i’ll be watching your answers, great question.
Their are 2 remedies for a sweating toilet tank. The first and best method is to install a toilet tank with a factory installed liner, they are much better than the liners you install yourself. The second method is to install a tempering valve (drawbacks are:valve will clog and H&C pipes must be accessable).