From my experience, a grilled cheese sandwich will get soggy for a few reasons. The first one being the type of bread you used (see Q2), and the second one being the fillings. You need to be sure you are using the right proportions. Any type of filling that releases liquid is going to add moisture to your grilled cheese. This is why I keep the rhubarb sauce to a thin layer in this sandwich and offer a side of sauce for people who like to have something to dip their grilled cheese sandwich in!