Leaves do two things: support the truck AND locate the rear end, so they're kinda like the links. Bags can't hold a rear end from moving all around (look under your truck and imagine what's left if the leaves were gone), so the rear needs to be connected to the frame via link bars. There are bolt-on kits to convert to bags and maybe even coilover setups for trucks, so I'd imagine one for an SUV is available or easily fabbed from the truck setup.