Door speakers are going to be a PITA if you are bolting them into the door itself. The "topography" of the door where the factory put 5 1/4"s is all screwy - you cannot just mount a speaker to it. Those little baskets are the key if you want a factory style installation - they are made to bolt to the door sheetmetal & conform to the surface. Otherwise, get creative!! Mount into the door panel & cut the door for speaker magnet relief.
HTH
Linc