Instead of foam could you not use springs under the pickup ears?
I likes a rear route... Nice wood body... Danish oil rather than stain?
I would be having a word with the body manf regarding the P route. what make and model pickup were they routed for? You may need some extra clearance if you want the halves of the P to 'crown' angle up, then down to follow the strings, following the fretboard radius. how about the J fit?