I've installed a few prehung exterior doors over the last few years, trying to flash and caulk the doors as best as possible. Unfortunately, none of these doors have roof overhangs to protect them from the weather, and storm doors on the outside are not an option.
In almost every case, there have been problems with leaking and/or rot, and now I need to repair or replace the door frames.
The door frame assembly really seems like a dumb design in the first place. It relies on the caulking/sealant between the sill and door jambs to prevent water from coming in, and then the wood sits right on the sill to wick up moisture.
If I can find some place to order them, I'm planning to replace the rotted door jambs with jambs that have a PVC bottom section to prevent the wicking issue (like the "EverJamb" at http://www.evermark-lnl.com /), then installing a sill pan under the jamb (like the "Jam Sill" at www.jamsill.com). But these still seem like work around fixes to an inherent design flaw.
So, I'm curious if anyone makes a one-piece door sill with upturned edges? Then the door jamb could overlap the sill edges, keeping the bottom off the sill to prevent wicking. Wood doesn't touch water, and there's no where for moisture to go but out. It seems like such a basic flashing detail to me, rather than relying on caulk between the jamb and sill.