Not sure about bumpers, boxes (I have aluminess) but plenty of options for roof racks these days.
Just installed a Rhino Rack Pioneer Tray on my E350. Love it so far. The T track makes it easy to make your own mounts, etc. I also used the SMB installed Thule tracks so the install was pretty easy.
Also: I had an issue w a cracked Aluminess bumper from frozen water in the tubes. Customer service was great. I talked to an actual human when I called and they didn't even bat an eye at repairing and repainting it. No charge.
2012 E350 SMB/Quad Van
2021 Chevy Colorado ZR2 Bison