well from what i read (i believe in that same link posted above) a box style top is the worst for creating drag. a tonneau is better for mpg then leaving the bed open. i like tonneau covers so even more reason to buy one in my case

 

Cab high camper tops are a 11% or so
worse than even the factory original open bed:

http://www.sema.org/Main/SemaOrgHome.aspx?ID=52546

 

Thanks again Hank,
and I stumbled on this http://www.4are.com/fuel.php

The sema article says "square cap" and that is very vague.
I have one of these

and I am really surprised that it has more aero drag than an open bed.
However I can understand more drag with one of these

Anyway, the cap does add weight. I would guess mine weighsat least300lbs.

 

Here's mine:
I just took the canopy off the other day and am in the process of seeing if my MPG goes up any...so far it's not looking like it is....

 

i have been trying not to drive so fast and i think i am seeing an improvement! normally i get about 48-51 miles out of each 1/4 tank but i have been trying not to drive over 2000rpms(i do city driving mostly) and after filling up i see im at 56miles and just hit 1/4 tank. seems to be working atleast something so small and cost nothing lol thats about 8.6 mpg give or take...when i was getting a little less then7.6 before

 

I get about 320 miles out of a 35 gallon tank, however even when it's on dead empty (or beyond), it's rare that I can pump more than 30 or 31 gallons into it, so there's a decent reserve. On the other hand, it doesn't budge off of past full until I hit almost 100 miles and it goes through the second half of the gauge alarmingly fast.

Still, that's only slightly better than 10 MPG with mostly city and country driving (about 40-45 MPH without many stop lights) and not much highway. I've just resigned myself to the fact that just turning on the engine will cost me about $5. I only use the Dodge when it has work to do and whatever it's carrying won't fit in my Mazda wagon.

I'll be adding a tonneau cover and some new tires shortly, so I hope to see at least 1 MPG improvement. New front bearings, brakes and U-joints may even help, too, who knows? But I don't think you're out of the ordinary on your mileage.

 

I get about 19 mpg on back roads and I'm running 33.12.50 tires.the only mods I have is 3 inch catback exhaust w/cheapo pace setter shorty headers and a 1 inch lift plate under the trottle body.Im not complaining. The ford guys I go wheelin with are always running out and I'll still have plenty. I must admit though there's something satisfying about towing a ford home after a day of wheelin! LOL

 

You have a 1998 360 in a heavy vehicle. Remember, gas was below $1.00 per gallon in the US (not sure what Canada's price was back than) so companies weren't as MPG focused back than. Your milage seems reasonable for the age and setup of the truck. Hypertech the truck and swap out all your fluids for synthetics as they come due. You should gain another 2-3 MPG, maybe more with a 2WD. Good luck, let us know how it turns out.

 

Someone looking to start a small business
could design a lighter than normal cab high camper top
with a few 'tricks' to improve the aerodynamics
that would increase highway MPG
rather than worsen it.

Even though full size pickup sales are slightly down,
the Dodge, GM, Ford, Nissan, Toyota combined market is huge
and the mini and mid sized pickup market adds even more.

 

I do not believe camper shells add anything but wieght, no matter how areo they are. If you put just about anything just inside the tailgate & then drive around at any decent speed where does it end up? Right behind the cab.
Cutting through the air makes the air circle in behind the cab, actually helping push the truck, not much mind you, but enough that a cover, shell, or those web tailgate do no good at all. Another example of this effect happens while riding in the back of a camper shell with window open then fall asleep. The fumes of carbon dioxide swirling into the camper will give you the biggest headache you have ever had.