Arctictraveller made a limb riser for the side of where his awning is. Not exactly what you are looking for but it will probably help. I suspect he doesn't have much of an issue as his GTVR isn't that high compared to a high top van.
I plan on doing to same on mine as well when I install my awning, I also plan to put some sort of protective edge along the sides of my hightop. I've noticed that the branches of slowly scraped away the first layer of coating on the edges of my fibreglass hightop.
2004 E350 RB 5.4L Chateau
4x4 Quigley w/ Fixed High Top