Can I Fit?
 

A sub with a top depth mount of 6" inches in a single cab 04 Ranger?

Anything is possible, what diameter is the sub. And if it's only one sub you can always make your passenger suffer. Passenger comfort < bass

Its a 10" sub

not with out losing footspace. i got kicker comps on sale and had to return them cause they were hugely tall. 6.75". i think 4.5" is about as tall as you can go to shoe horn a 10" in without losing anything

Depends on how much foot room your willing to lose :)

Build a down firing box, the demensions work better from my experience. I built a box for 2 12" cvrs in a single cab f150, like 2-3 cubes per sub, no foot space lost. Just gotta play with the numbers and design. With just one 10 I dont think you would loose much room.