I simplified mine, I took an old wood window frame, with glass, cut down the frame where the sash weights were and then built the melter to the dimensions of window. I had an old metal drip pan from a freezer I used to lay the wax in to melt it, that was half the size of the window. I then built it with a slanted bottom so the low part of the drip pan let the wax drip into a bread loaf pan with a screen and filter over it. I put hinges on the window frame so the whole top opens.
I figured out to make the box dependent on the glass size.
And you can improve yours, take a plastic tray/bowl that comes in some TV dinners and use it for your wax pan. Its better, it flexes so the wax ingot pops out.