I use a combination of the amp research powered step, and a step ladder.
If it's just a regular person hopping in our out of the van, we just use the power step. The TOP of that step is 22" off the ground, and it's just shy of 13" to the inset step in the van doors.
If we're loading the dog or camping, or someone with a skirt needs to get in, then we just deploy the step ladder, which just happens to FIT PERFECTLY in the instep in the doors.
This step ladder also serves as a gate for the dog, when we stop we can open the cargo door and he stands right at the step but doesn't try to get out. It's a visual barrier more than anything, but I could easily secure it and make it more stable. He has not yet pushed on it. He also will not try to jump out of the van unless the step is there. We've trained him to be wary of heights like that, being a lab and prone to hip issues.
(side note: when we get in the jeep, he sits near the drivers side door and waits patiently for me to run one arm under his belly and the other under his neck to lift him up into the jeep and then he gets in the back.)
BTW in case you don't know, the amp power step retracts to flush against the body when the door is closed.