B+ motorhomes

We spent the 8 weeks of November and December on the road in our 2003 TL 211S. It really performed flawlessly as we toured through CA, UT and AZ. The Achilles heel for us is storage space despite the fact we have a Yakima Space Box on top. We are a sporty couple and want to bring our bikes (with attendant helmets, shoes, etc), snow shoes and/or XC skis (with boots, etc), and on and on. We actually manage well enough but climbing up that ladder in cold/windy/icy weather gets old in a hurry. I am thinking about a cabinet box that could be body mounted on the driver's side of the center rear door, something that doesn't stick out past the existing back door steps. Anyone have ideas?? We can't and won't use the cargo boxes that use the hitch receiver, as that would interfer too much with use of the back door and/or be unavailable because our swing-away bike rack is using the hitch receiver.