If the camper will be on the truck all the time, you might try the felling wedges. See this link: https://halethorpephotography.smugmug.com/Truck-Camping/Towing-and-Weighing/ Scroll down and you will see my implementation. This has worked well for me for 2 years including a cross country trip. They are way cheaper than the stableloads. I think I paid about $10 each at tractor supply. They are less convenient than the stableloads to dis-engage though, which is why I ended up buying the stainless steel stable loads.
As for upper or lower springs, my thinking is that the lowers engage first by design, so starting with the lowers seems logical to me.
As for drilling the springs, slow slow slow. Use a cordless drill on the slow setting and turn the bit as slow as possible. I started the process using the corded drill, and it just would not go slow enough and burned up the bit immediately. I went the the cordless drill, with a standard steel bit no less, and it walked right through that spring steel. And spray it with WD40 or some other lubricant occasionally.
Good luck,
Joel
