You just need to take a single hacksaw blade and start removing material until the Eonon unit fits. Just start with the obvious obstructions and keep trimming until it fits snugly.
As far as the backup camera Crowz and I both used the Chuanganzhou unit from Amazon. Small unit, less than $15 and good picture in low light.
http://amzn.to/2ibYp9j
Here is his DIY install link.
Backup-Reverse Camera | Crowz Nest
