Hello, I am looking for some advice. I am planning to build a few doors. One will be an exterior door (which I hope to find a way for some minimal insulation) for my son who is building a tiny house in the Maine Woods. Others will be interior 4 panel replacement doors for an olde,r first home my daughter recently purchased. I have done only one door in the past. This will be a learning curve for me. The previous door that I made I used a plunge router for the mortises. Currently, I have a bench mortiser but I do not think this will be a reasonably efficient tool for approximately 3" deep in mortises in White Oak. While looking for ideas on YouTube on methods to accomplish this I came across a Porter Cable Lock Mortiser which seems to be an efficient way to accomplish this. I would appreciate any education on anyone who has used a router driven lock mortiser. One issue if it is in fact the proper tool is where I may find a used one for sale. I imagine some may direct me to the Festool Domino but at roughly $1600. it seems a bit overkill. I apologize for this long winded description of what I want to accomplish. Your comments/advice will be appreciated. As an aside my son has experienced real temperature of -15 degrees in Maine this winter thus the search for ways to insulate an exterior door. He really wants a hand crafted door. Thanks in advance for the advice.