7 in the rear is a challenge. I am down about 5.5 in the rear and to go further, you would definitely need to relocate the gas tank and do some other work to have any suspension travel at all. Plus shocks get wonky - it's hard to find anything short enough that are actually worth spending money on. At 5.5" static, I had to make a new crossmember over the driveshaft, cut out the crossmember over the diff, C notch, modify the fuel tank filler, relocated the shocks, and make a new exhaust over the axle. At 7" dropped, you will probably need to modify the floor in the rear to clear the diff, and you would definitely need to relocate the tank.
Helper bags are not your problem, nor your solution. It's just for leveling if you run a load. I ended up just going with stiffer leaf springs. They don't actually make the truck ride better, unless the suspension is soft enough that it is hitting the bump stops or bottoming the shocks out. The added spring rate/ride height keeps the suspension off the stops a bit better. Most people have the suspension set up too soft (stock leaf springs) for being low, and the Tahoes are even more sensitive to it because there is so much more weight over the rear axle.