I saw this post obviously a little late, not sure if you have solved this problem or not. But I have 2001 Exp. EB. and do not have a backup camera either.
BUT, before you go cutting into the truck and stuff, I discovered another viable option for a lot of us 1st or 2nd gen owners that do not have this option on our vehicles.
https://www.hsn.com/products/pearl-rearvision-backup-camera-and-alert-system/8380684
Its a backup camera that is embedded into a licence plate bracket, its a little more pricey than one could want to spend, and not sure if there is others out there like this. But wanted to share it anyways to let people know there is another possible option.