Here's a suggestion for a body.
The Proline F650. I got two of those last year because they were the longest 1/8 MT bodies I could find. It's almost 20'' long and from the middle of the fenders is 14''.
Here's a pic of the two bodies taken before we started using them. After a year of hard bashing, they need to be replaced. They don't look like that anymore
If the hump of your truck requires a taller body then maybe the
HPI Bounty Hunter.