@Brian Eastman
I like your post, I understand the points that you are making and I know you are very knowledgeable, as this is your area of expertise. That is primarily why I wanted to reply and understand further.
I know that one of the biggest problems with 401k loans is job security, as the note will become due within 90 days of a job change, or the balance will be treated as an unqualified distribution (and taxed and penalized).
My question is regarding the double taxation issue; I think 401k loans are generally considered last resort options because the money is paid back with after tax dollars. However, in the event that a person is planning on getting a loan regardless, every loan will be paid with after tax dollars. With a 401k loan, however, while the borrowed money won't be appreciating (or depreciating for the matter) in the market, it will be getting the interest that you pay yourself, rather than some other finance company.
I'm sure there is a factor that I'm not considering, but seeing as the OP is probably going to get a loan anyway, I think that a 401k loan might be one of the best avenues, with the stipulation that he considers his occupation within the company very secure. I eagerly await your thoughts.
Chris Haydis