Hi, Valleyview. A few short answers:
(1) A few forum users with pre-owned Interstates inherited rear door-mounted ladders and, while we haven't heard anything negative about them, I myself would not install or use one. The sheet metal of the door was not designed to bear the kind of weights involved and could deform under such loads. I researched this more than a year ago but upon having concluded that we were not going to install such a ladder, I discarded my info sources, so I can't point to anything definitive right this moment.
There are two ladder alternatives:
(a) We use a Telesteps 1400E, which we keep bungee-corded to the rear of the passenger seat where it only consumes about two inches of depth. We find it superior to a fixed ladder because we can move it where we need it.
(b) IMO the best fixed roof ladders made for the Sprinter are by Aluminess (
here). They mount to the gutter and anchor under the chassis and thus do not pose the same sheet metal deformation risk.
(2) I don't recall anyone reporting using a cargo net. I'm not sure how you'd attach it securely.
(3) I also don't recall any Interstate owner using a roof box, although they are popular with Sprinter owners who do not have fixed roof air conditioners (e.g., Roaming Robos; photo
in this post). I don't know how they could be made to fit well given the roof configuration of the Interstate.
Many owners report hesitancy to use a hitch box, and yet I've never heard anyone complain after-the-fact about *length or size* issues. I've heard them complain mightily about *quality* issues of commercially-available options, yes, absolutely. If you want to avoid the "big blob" effect of a large hitch box on your back end, there may be a minimalist solution that would fit your needs without making you uncomfortable. My husband and I custom-built a hitch carrier that only extends us by 16.5 inches, and yet it opens up a world of cargo opportunities that we just didn't have previously. An additional 16.5 inches is utterly undetectable while driving and has very little impact while parking (although I do decapitate the odd shrub when backing into commercial parking spaces with fringe landscaping).
You have only a few posts to date and I'm not sure how much research you've done on this forum, so here's a re-paste of my Imgur link to our carrier (the sides were later trimmed out with DOT C2 reflective tape;
here are some blog posts on its construction). Not only is it a carrier, it serves as a "back porch", rear step, and the open portion (where the dog sits in the photo) is where I plan to lash a new inflatable kayak that we just bought. We refused to accept a large hitch carrier and this turned out to be the perfect compromise for us.