CD changer in V70 II

Hello, can someone tell me where best to install a third-party CD changer (Becker Silverstone) in the V70 II? My workshop tried it under the passenger seat, but it was supposedly not possible. Then they put it under the rear boot cover. For this the spare wheel had to be replaced for an emergency wheel and the cover mat was cut. However, the place is extremely unfavourable. It is a 6-fold changer, that is, you have to put all noses long on the box. What does it mean to clean out the trunk of the car? Can’t accept it like that. Besides, the workshop smashed the changer when it was installed and now has not received a replacement for 4 1/2 weeks! And Friday we are going to Brittany! Who can help???