I would not want a mega. A CC with 8' bed is already loooong.
Second, and most important, what do you mean that the weight will be near capacity? Does that include propane, water? How about any modifications such as accessories the manufacturer did not include, mattress upgrades, solar, extra battery, generator? Then there is what is typically about 1000# of "personal" items such as lawn chairs, BBQ, clothing, food, cooking/eating gear, tools, toiletries, towels, sheets/bedding, electronics/cameras/laptop, passengers, etc, etc.
You can easily find your rig weighs more than 1500# over the manufacturer's claimed "wet" weight.
If all of that is still within but near max load, the first place to look is tires. You don't want to be overloaded or at max. You might be able to upgrade just the tires or might need to go all out for 19.5 rims and tires.
Suspension upgrades are almost always going to help or be absolutely necessary. I would put airbags last on the list. Mine just gave too much sway but others have had success with them. Instead I would start with something like Timbrens. That will help level the ride and keep the headlights from blinding oncoming traffic. Next if more is needed, I would look at SuperSprings. They are relatively cheap, and can be adjusted and installed by the owner. Heavy duty shocks can also help but if the suspension can handle the load, they may not be needed.