The 10-12 times a year I tow my 5th wheel just didn't justify the expense of a box (at least to me) to try and increase my mileage when towing. Maybe if I did a lot of OTR like Rhino or others I would try.
I regularly get 18 in town, have honestly hit almost 24 (empty) on the highway IF I stay at 1900 rpms and does what I need it to in stock form so I'm good with that. up
Good luck in your quest. luck



Tim

'71 Charger 383/727
'17 Challenger SXT (Wifeys car wink )