A reskin door job came in with familiar rust volcanoes on the lower edges of both doors, a sight we've seen all too often even in these days when every car is garaged. The reason they rust there on the lower two inches of the doors is that water gets into the doors and seeps down inside between the door skin and the piece of steel its wrapped over. This piece isn't painted on the inside and neither is the door skin. Between these two pieces is a gap where water drains and can go no further, so there it stays until it creates those little crapuscules we would call Worcestershire Wrot. For less than ten bucks and an afternnon not watching the Seahawks lose another one, this malady can easily be averted. It is dead simple to remove the inner door panels where we can then see the crevasse we need to seal. If it is still very damp that can be cured with a hair dryer, being careful not to heat it so much that we blister the paint. When all is nice and dry we can tackle the "hard" part.
If it is at all rusty there already we can remedy that with a rust converter. A small bottle of this is about five bucks and it converts rust, iron oxide, to iron phosphate. The rust then looks almost like porcelain and will not rot any further if there is no moisture to promote more rust. Now while the door panels are still off it is a good time for a step two which is a bead of your favorite water sealer around the inside of the door between the wood and the door skin. A good choice of sealer would be a flexible silicone like GE clear silicon. Do not forget to do the outside of the wooden frame where it touches the metal of the door. Two hours and ten dollars is a bargain compared to the charges one can expect re-skinning your doors.