I ran into the same problem, there really are no air shocks short enough to use on a lowered truck, part numbers are pretty limited. Good luck with it

 

Here's my first one today. Unfortunately, I only had time to do the drivers side. Have about 3/4 inch below c notch. Hopefully my ridetech coil overs won't allow the axle to touch, but just in case I think it'll be functional.

 

Looks good! You want the bumpstops to hit before the suspension is over compressed, that is why they are there. Will you hit them before your shocks or springs bottom out?

 

There is great misconceptions about trailer towing that leads to people using (or thinking they need to use airshocks. I've towed a lot of various size trailers from small utility trailers to boat trailers to double axle enclosed car haulers over the years and this is what I've learned from research and experience:
1. First make sure your hitch ball height matches the trailer tongue height with the tongue parallel to the ground. The trailer should never ride nose down or nose high. If you are using a receiver type hitch (you should be if using a capacity rated hitch for anything larger than a lightweight utility trailer) you can purchase hitch tongues that mount the ball at various heights above or below the receiver.
2. Load the trailer properly to produce the recommended tongue weight. The tongue weight if not specified should be no less than ~ 60# for a small single axle trailer (you should be able to lift the tongue by hand with some effort to move the trailer around) to no more than 500# for a large multiaxle trailer. If the trailer is causing the rear of the truck to drop further than what it does if two men stand in the back of the bed then it likely has too great tongue weight and the load needs to be redistributed or the axles moved forward if the load location cannot be changed. Note that the maximum tongue weight is 1/2 the load carrying capacity of a 1/2T pickup so it should not overload the rear springs unless VERY lightly sprung.
3. If you are using a lightly sprung rear truck to tow the same trailer (such as a large travel trailer or a loaded car hauler with a high tongue weight) then instead of spending the money for air shocks, buy a torsion bar weight distribution hitch setup. The WD hitch will actually LIFT the rear of the tow vehicle. Even with the air shocks too heavy tongue weight distribution can result in raising the front of the truck so it becomes light, enough so that you can lose steering control over bumps and front brake effectiveness, a very dangerous condition. Air shocks are a band-aid, a VERY DIRTY band-aid.

PS: there is a big price difference between QUALITY built shocks and CUSTOM built shocks, I recommended quality built ones, not custom built ones, unless you have a very unique situation or application, it's unlikely you need custom built ones (just to point out the difference, a set of 4 garbage big box store shocks cost about 160.00, a set of quality shocks will cost about 500.00 (and outlast 3-4 sets of the garbage shocks), a set of custom shocks cost 3000.00 to 20,000.00 depending on complexity (the custom ones on my Solstice cost me 4K, I would NEVER spend that much for shocks for my truck, but they are the difference between winning and losing on the Solstice!). The difference between BB shocks and quality shocks is like the difference (price and ride) between bias ply and radial tires. If you don't want/need/afford to use radial tires you probably don't need shocks at all, so it doesn't matter what you put on your truck.