I'm saying you can have the cadaver dogs alerting to cadaver odour in the McCann's apartment and hire car, and still have CB killing Madeleine at his place. This can be achieved by having a cadaver being placed in the apartment and CB abducting Madeleine from the street i.e. a complex situation.
Complex indeed, although not without its merits.
Certainly the dogs didn't get it wrong, they rarely do and, backed by cutting edge DNA analysis of the fluids, well your theory certainly holds some weight.
Having said that, finding a different cadaver on a quiet holiday resort, then placing said cadaver in the apartment temporarily for an indeterminate length of time, then subsequently removing the now defiled dead person and successfully disposing of it, would provide a challenge, and would almost certainly require a receptacle larger than a tennis bag and at least two people to manually handle (given current Manual Handling Reg 1992 - although I doubt adherence to any UK Health and Safety legislation would be upper most in their minds when they've got at least one cadaver to shift about, more likely two in this scenario).
This also doesn't explain, if the McCann's didn't 'do away' with poor wee Maddie's body, why would they feel the need to import a deceased person and leave forensic trace.....hang on.......I'm thinking this out.......so......MM meets with a terrible accident and, being DNA savvy, the parents know that they would either need to forensically clean as best they could, or contaminate the residue. So, they spirit MM away in the manner that we've all agreed upon universally, then either run someone over or cruise around looking for someone dead, find an unwilling and unwitting participant, drag them through the patio door (or through the open window, although, again, manual handling would prove a challenge), place the cadaver in various poses around the apartment (like [Name removed] Bueller's Day Off - classic movie), then drag said carcass out in reverse and dump it in a....bin......or......car.....or.......furnace. A furnace. Where locally has a furnace? A furnace manufacturer?