About a year ago, I asked this question after searching reviews on places on I-10, and finding quotes like "make sure your .357 is under your pillow", or "keep your .45 handy".
Here is what I did: There is a KOA in Van Horn for about $38-40/night. I'd either go for that one, or skip El Paso altogether and head to Las Cruces and find a decent RV park there.
Things change though. I can read RV park reviews and tell if a park is not being maintained, or if a park has been cleaned up, perhaps under new management.