DIY single sidestep for sliding side door?
 

I own an 89' E150 4.9L and as title suggests, i'm looking for a single side step for the sliding side door.

I'm sure I could figure it out myself but would like to hear what others have done before I try to make my own. Just needs to be sturdy/big enough for my senior black lab to jump on to get in, there is an interior side step but was planning to box it up and use as a wet area/storage. I'd think hoop steps would be too small and I can only find pairs of runners (at cheapest $150) but would just need the one. Any ideas anyone?

TIA!