Soggy = too much liquid. There are three main layers to a moussaka, and the problem could be caused by any one of them! 1) Ragù: make sure to cook it down so that a dipped spoon can stay upright for a bit. 2) Eggplant / potato / zucchini: Salting, drying, then baking them in the beginning will solve your problems with soggy vegetables. 3) Béchamel: Make sure to use enough flour and starch. It's normal for it to be runny before being cooked.