Many years ago, when Petersen's Photographic first began publishing, they were known mainly for their DIY articles. Most of those articles were written by a guy named Parry C. Yob. At one point, they published a book that reprised some of the best DIY projects.
One of the plans in that book was for a dry mount press. My recollection is that they were suggested embedding nickel-chrome heating wire in a platen made of portland cement. My reaction was that while the though was good, the idea of a DIY drymount press wasn't all that practical.
But if you could find that book today, it would give you detailed plans.