For some reason it's impossible to find commercially available backshells for the XT-30 series of connectors. So here goes.
These are intentionally tight and will often retain with friction alone, but a drop of CA does wonders for permanence.
The Plug cover has retainers internally, the receptacle fits flush or close to.
Walls at 0.16 for strength, use brim internally and externally for stability (with 0.2 gap). Support not needed