I just installed Carr hoops on my van. I ended up passing on the barn door step as the grey water tank was in the way for me too. Having dropped my grey tank before I know how little room there is to work with in that space. To install the Carr hoop you'll have to remove the tank and install the step, I'm not sure there's enough room to get the tank back in with the step (mounts) there.
I opted to stick with this instead:
2003 E-350, 5.4 V8, 2x4, LSD 4.10, WeldTec 6" lift, SMB, Penthouse
2016 Beta 500 RS
2003 Honda XR250R (retirement trail moto)