I am looking into buying another minivan and want to install 3 cargo boxes on the hitch (total of 40 cu.ft.) and a 4-bike rack on top. I estimate total weight to be 620-650 lbs, so let's say 700 lbs.

Is this possible? Would the problem be with the hitch structure itself? Or the attachment points hitch-to-chassis? Or chassis strength itself?

Since this will be a cantilevered weight on the rear axle - I guesstimate 1000 lbs -- will I be exceeding Rear GAWR (Gross Axle Weight Rating, and I don't know what that is in lbs)? If not, I can try to address suspension geometry with air-bags.

As an option, I can mount a roof-top cargo carrier, and lighten the load on the rear hitch by 150 lbs. So hitch load would be 500 lbs = 800 lbs cantilevered.

What would be the penalty in MPG for a Roof Cargo Carrier?

You can't put that much tongue weight on a Caravan, the stock rear springs will not hold it. You will be resting the rear axle on the bump stops and they are likely to fail. These vans can tow alot of weight but are not made to hold alot of weight.

I installed an air bag system in my van to handle extra weight. I use the Air Lift system with an onboard compressor. I tow a large pop up camper plus all the added gear inside and it caused the factory bump stops to fall off. Now my van stays level with the loads you are describing. The best part about the onboard compressor is that I can change the capacity on the fly and also tone it down once we are at the campground or the van is unloaded.

The van can handle the weight no problem, the rear springs cannot.

Thanks for the input. I realize that I may add airbags. I have used them and have a good feeling on their benefits.

Good to hear that the chassis / suspension / brakes can withstand this weight hanging off the back, plus bouncing / inertia etc. I might just use a Class III hitch, if I can make it fit. Or I can fabricate something customs to hold up the rear platform on 2 points.

Thanks for the input. I realize that I may add airbags. I have used them and have a good feeling on their benefits.

Good to hear that the chassis / suspension / brakes can withstand this weight hanging off the back, plus bouncing / inertia etc. I might just use a Class III hitch, if I can make it fit. Or I can fabricate something customs to hold up the rear platform on 2 points.

For around $450 you can get the same airbag system I use:

http://www.jegs.com/i/Air+Lift/022/59560/10002/-1

http://www.jegs.com/i/Air+Lift/022/25592/10002/-1

I have had a complete V8 truck engine inside my van and I was able to maintain level ride height and no bottoming out. My trailer has 300# tongue weight and with another 2-300 in the back plus my kids and I could easily maintain level height with no bottoming out. Right now, I keep about 400# of tools in the back of my van at all times and it takes it in stride. I cannot recommend this highly enough if you're gonna work your van on a consistent basis.

As for mileage, I still can maintain over 16mpg in mixed driving while towing my camper and all gear loaded even with the A/C on. One thing I do suggest is to make certain your can has the auxiliary transmission cooler as these vans are not known for having a strong transmission. I tend to pamper my van and driving it with that thought in mind at all times and I have yet to have a single issue.

As for tongue weight, I am not sure that even with a class 3 that the mounting points can withstand over 500# for any length of time. Technically, they are bolted to the unibody rear subframe points and there is not a whole lot of metal there although any competent welding shop should be able to figure out how to weld some extra support in there. After 2 active camping seasons with my van I have had 0 issues with the from the mounting of my hitch.

Properly equipped this van will shock you as to how well it can be put to work. The one thing I cannot stress enough is to make sure you become anal on maintenance and be mindful of the transmissions weaknesses. It should do exactly what you want as long as you are mindful.

Understood on the transmission and other points. My buddy, a previous Parts Manager at a Chrysler dealership, has been very informative in all matters Chrysler, transmission, electrical and others. I used to own a 98 Concorde, and did the work myself on it.

I have been inquiring with Odyssey and GM minivan Forums as well on same issue, and thought that since Chrysler minivans have the leaf springs, while others have coils, I thought that maybe Chrysler minivans might offer a chance on my intended set up.

I think it is time to look under a Chrysler Minivan's rear.

Problem is that it is a monoleaf and is geared towards ride quality not load ability although that is not a problem considering these are the only types that will allow the airbag installation.

GM only offers airbag on shock and I doubt Honda has any ability to add airbags outside of mega-custom.

EDIT: I should also add that I own a 2002 Grand Caravan Sport and is is the best of all worlds. I can have 7 passengers, all my cargo and then some and get great mileage. I average 19MPG in mixed driving and it will get well into the 20's pure highway. Other than some minor issues (which are common) it has been a great van and very reliable. I strongly recommend one for hte use you are intending, the Chevy and Honda are just not able to be upgraded for the task.

Another important point on the airbag suspension is that when the airbags are set to their lowest safe PSI they do not effect ride quality and height so that the van acvts like a completely stock passenger vehicle while when it is loaded to the gills it retains a comfortable yet level ride.

Understood. Is there a monoleaf on each side (2 in total), or one single monoleaf (1 in total) that goes from one side to the next?

Another thing I was checking on Curt Hitches -- Curt requires stabilizing straps on any non-trailer hitch-mounted loads on GM minivan, but not on Chrysler.

GM only offers airbag on shock and I doubt Honda has any ability to add airbags outside of mega-custom.

Honda guys use them conventional (inside the coil, Firestones 1000). Many GM vans have load-leveling air suspension, which yes, can be replaced with air shocks.

Another thing I was checking on Curt Hitches -- Curt requires stabilizing straps on any non-trailer hitch-mounted loads on GM minivan, but not on Chrysler.

Scratch that. Curt actually requires straps on Chrysler, Ford, GM minivans and recommends them on Honda. Again for all non-trailer, i.e. hung loads.

Hidden Hitch does not say anything about the Stabilizing Straps.

Has dual leaf springs. I don't carry loads other than the trailer so I am not sure about my hitch, I have the Hidden Hitch.

Airbag inside springs sounds better than air shocks, I hate them, they never last and always fail when you have a big load. I would not recommend anything but airbags for your application.

Has dual leaf springs. I don't carry loads other than the trailer so I am not sure about my hitch, I have the Hidden Hitch.

Airbag inside springs sounds better than air shocks, I hate them, they never last and always fail when you have a big load. I would not recommend anything but airbags for your application.

How many leaves on each side for Gen 4?

All have single springs, they are not designed for weight capacity, just comfort.