Generally, 1988 is the year the campers started being made to fit the narrower tailgates.
1988 (not 2007) is the year Chevy went to the narrower tailgate and stopped making the old “square body”, although the crew cab and Suburban kept the square body through ‘91.
Dodge kept their square body until ‘94.
Ford kept the square body until ‘98.
Before that all full size American tailgates were 65 inches wide.
They’re now down to about 60.
Space between the wheelwwls isn’t the issue, that’s still four feet.
Many campers have a little “kick out” that uses the space inside the truck box behind the wheel well.
That’s where the interference is.
Sometimes you can just slice it there and narrow it a coupe inches and make it fit.
In my case the fiberglass shower enclosure was right up against that area and I had to section it and re-fiberglass it to make it fit.
Anything fits anything if you want it to.