With this in mind, perhaps Madeleine's body was never in the boot of the hired Renault scenic - maybe clothing and equipment used in the movement of the body was / is the source of the cadaver odour and blood found in the vehicle...
I personally can't believe that a few weeks after Madeleine died, that the parents would risk moving the body of their daughter from its hiding place where it had remained undetected for weeks or a month or so, and transport it in the boot of a hire car they were known to be using!
But, in the knowledge that the cadaver dog and blood hound were coming from the UK, I can see why the remains of Madeleine would need to be exhumed and repositioned in a secluded location not easily accessible to the dogs - it makes perfect sense that if the body had been originally in the shallow grave of the rear garden of the derelict building, that the cadaver dog and the blood hound might show positive alerts inside the derelict building and it's garden because of its close proximity to St Vincent's church which the McCann Parents were known to have been frequenting soon after Madeleine vanished from the face of the earth...
Thus Madelienes remains were exhumed, and transferred and dropped into one of the vertical drains situated on the ledge the other side of the boundary wall of the derelict building...