I've heard that there are RV parks that only have 50 amp outlets (no 30 amp), but I've never actually seen one. I doubt you'll need the adapter, but as you say, it didn't cost much.
MikeK - Glanced at the photo of the trailer and brain said, "Hmm.. Something not quite right there..." The picnic table is green, and is situated such that at a glance it appeared there was grass showing through completely empty wheel wells.