I highly recommend Boise spring works to custom build a set of back springs based upon the load you are going to carry. I tried airbags and they were a joke compared to a good set of custom springs. They are also reasonably priced and you they can build it to your truck dimensions without them seeing your truck. I had them shipped in and took them to a shop for install. I typically run my FWC on the truck or a leer camper shell. Without the weight they are stiff, but I have no reason to take off the FWC now that I found a long term solution for the added weight.
My 2015 taco has a 2.5 inch lift on the front (adjustable Bilstein's) and Boise Spring Works built in a 2.5 inch lift on the back so it sits level. I run 285 BFG's on my 2015 taco. It is ready to go anywhere and rides like a dream. I also had to find some Bilsteins shocks for the back as the OME's bottomed out, but in all it is a very reasonably priced suspension upgrade that should last a long time. I stuck with a 2.5 inch lift as the service manager at Toyota told me not to go over 2.5 as it will start to screw with the long term wear on the drive train. Even with the 285's and a loaded truck, it has plenty of power and will stop just fine.