The reason for the deadbolt and key is simply to avoid dealing with a knob, which sticks out, e.g. hanging in the breeze as I drive down the road. A closer might be a good idea, I agree. Anyway, I am not locked into doing this with a house door, it's why I asked. After all, I have the receipt and can simply return it to Lowe's if that's the best move for me. However, with respect to installation, that's pretty easy actually as I can frame out the rough opening, plug it in the prehung door assembly, seal it with caulking, run screws, and presto, it's done. FYI, I'm actually a fairly decent carpenter.
With respect to the Kino mobile home door, thanks for pointing me toward them. I will investigate further.
Regarding screen doors, I also purchased one of these retractable Larson units http://tinyurl.com/c3e2b6t
while I was at Lowe's the other day. This thing is pretty sweet because it folds like cloth blinds into the pocket, and in the case of the oputswing door, fights neatly into the rails and stiles of the prehung door, but on the inside of the box. It would be a very sanitary installation, believe me.
Anyway, I will investigate further, but it seems a polyethelene skin and polyurethane foam door crafted for a mobile home is somewhat flimsy and much less secure than the steel door equipped with deadbolt. Regardless, let me mull over your thoughts and check out these Kino doors.
Many thanks for sharing your ideas!