We haven't heard from you for a while, always good to get longer term feedback.
A few things related to Erb have happened while you were gone, including me buying a set of his springs to test as folks seemed to be getting very differing results with them. Here is a link to the thread on the test and results:
http://www.classbforum.com/forums/f5/erb-spring-for-lifts-warning-6871.html
IMO, you results confirm what I suspected after the testing. Erb is making his springs to still for their size and load so the actually yield when being put in with spring compressor (that is why the varying results), and then sag over time. He is getting stiffness by over heat treating and using fewer coils and overstressing the material.
As for options, the Moog spring mentioned in the link will work. They are bigger wire, more coils, stock length and are essentially what we have from Ottomax that we got years ago. They will give about 1.75" lift over stock, or about 35.5-36" at the front wheelwells. Adding a 1/2" spacer would give you and inch higher, but starts to affect the alignment. If you were OK with handling before, you could do that. Other than that, you would be into another custom spring and have to have someone make them. You would want to be identical to the Moog spring but about 1/2" longer, with same wire size and material and number of coils.
The shocks thing is very common in the Chevies. All the aftermarket brands tend to use their own upper mounts which don't hold up. The solution is to use the stock GM upper mounts which will hold up fine with aftermarket shocks. I don't know if Bilsteins come with the GM mounts now or not, ours did not, so we used the GM ones when the Bilstein mounts failed in 300 miles.
Re the model year. 2003 was the model change for the vans. The 2003 up has longer springs than the previous versions. There is a possibility that a 2003 Roadtrek could be built on a 2002 van, so check the doorpost for the actually GM sticker to determine model year.
Unless you want to go very high, you don't need new control arms and such. I am not a fan of knuckle lifts like that, but others here like them. Getting up a couple of inches has been fine for us.