I'd ordered too much 1" galvanized pipe, which we had used for the deck supports. After making some sketches it turns out we had enough to construct a ladder for deck access. We only had to order some structural pipe fittings and flanges from McMaster-Carr (see Links).
The highest rung on the ladder would span 2 of the vertical deck supports.
We removed the support flanges and slid on the highest rung wih its fittings.
After adding a second rung, the support flanges were replaced. This rung has 2 T-fittings which will in turn hold 90-degree fittings from which the side rails will extend.
(90-degree fittings not shown. Next picture shows what I'm talking about.)
The completed ladder. I was pretty proud of my design until I realized that the second rung (red circle) was too close to the bus, not allowing our feet to fall naturally and securely on the rung. Rhonda came up with an alternative design that allowed us to utilize the existing pipe fittings and rung.
New configuration, side view.
We re-arranged the order of the flanges and fittings on the #2 rung, and managed to move the rung away from the bus body.
The side rails are continuous 6.5' sections of pipe. Near the bottom we added a 3-outlet fitting and a flange to the side of the bus.
We fastened beefy, steel grab handles to the deck for added support & balance for ascending/decending to/from the deck.
For added safety we applied gritty 3M non-skid surface adhesive tape to the ladder rungs and deck approach.
New configuration, front view, with non-skid applied to rungs.