Yep, I tow a 1700lb Aliner with a Chevy Cobalt SS 2.4l. I've installed an Injen cold air intake (with dual e-rams and a "helper" battery), an equal length header, b-pipe w/high flow cat, and Corsa Touring Cat-back exhaust, and a tranny cooler. I then sent my ECM/TCM to Wester's garage and had them tune the computers for my modifications and it's intended use.
In case you're wondering, E-rams are very high speed (23,000rpm) ducted electric fans positioned in your intake. They only run at wide open throttle (when you really need them), as they draw too much current (120amps for both) to run all the time. They work by slightly pressurizing your intake charge with about 1lb of boost each. They're good for a dyno proven 12hp on my 4cyl engine with supporting mods - your results will vary. They were supposed to release a v8 model (the ultra-e-ram) a couple months ago. It's claimed to add about 30hp on your avg. street v8 - for less than $1,000. They won all kinds of awards at this year's SEMA for it (best new product,) but they must be having problems with it cause they haven't released it yet.
The result of my mods was a car that gets better mileage, has more power (.7 sec quicker 1/4 mile) and a much more capable tow vehicle that's more fun to drive. I averaged 22.7mpg towing through the mountains (at the legal speed limit) on my last vacation. It will get 25-30mpg towing on level ground. I've hit 39mpg on the interstate, though I usually average about 30mpg around town when not towing.
The down side is that I'm now limited to premium fuel only, but that was at my request. They'll tune it for lower grades of fuel if you specify, though you'll get less performance improvements.
I didn't do the mods for gas mileage alone, that was just a bonus. There is no way spending $2,200 on performance mods would ever pay off, especially since the car was very fuel efficient anyway. I did it to improve my car's towing ability and to drop my 1/4 mile time from 15.73 seconds to right at 15 flat. I'm logging a little over 20k miles a year. Let's just say I'm averaging 3mpg more. This would net me a 60 galons/yr fuel savings, or $210/yr @$3.50/gal for a 10 year payback.
By the way the e-rams are strictly a performance mod and didn't help mileage any so you can subtract $600 from the $2,200 in mods. These numbers still don't work on gas savings alone. However, anytime I can stick it to those OPEC "Gentlemen" (euphemism inserted to avoid getting thrown off the board) who's funding the murder of our young troops (by using less gas), I'll take the opportunuty to do so. Money comes cheaper than blood.