Custom...
always liked the BOL KAs, bought a KDC-17 new in '74, have another one now, along with a KDI-17 and a BOL portable 17. They all have the same motor, and we don't use all those other cycles anyhow...they do a fine job if loaded right.
Agree it's not likely to rust, you can touch it up periodically, we kept the rust at bay on our old Volvo 240 for years just by grinding and painting all the rust spots every fall. If truly concerned about the chips, why not just do a door transplant, shouldn't be all that hard to find a good KA 18 door?