as for the 0.75 MDF, it is made for that. i made this program for my own use originally, not to distribute. so theres certain things you may fine questionable, for example, the slot port displacement calculator is actually an "L" slot port displacement calculator.
to calculate a port without the port extension (the piece of that makes the "L"), simply plug into this:
internal port heigth x (intenal port length - wood thickness) x (internal port width + wood thickness)
^^^^ that assumes the port isnt in the middle of the enclosure, but on the side of it, like the example in the link in my sig. if its in the middle simply double the wood thickness in the port width part.