Les "back in the day" late 90s we towed a 24 foot Odyssey (no longer in business) 5er and a 24 foot Coachman 5er with a shortbox Chevy. This was before the sliding hitch came along. I measured the distance from the center of the pin to the corner of the 5th wheel added 2 inches for a little clearance which indicated that the center of the jaws on the hitch needed to be about 8 inches behind the
axle center. Both rigs towed extremely well with no noticeable difference between the shotbox and a long bed with the hitch mounted over the
axle that I later bought. I don't have any idea what the dynamics would be on your Dodge. I once had a "truck" salesman tell me you couldn't tow a 5er with a shortboxtruck with my shortbox Chevy hooked to the 24 foot Coachman right in front of us. At that time I had probably pulled the Coachman about 30,000 miles with the set up as detailed above. We then had an interesting conversation. Lee