I purchased some 1.1″ heavy-duty heat-shrink with adhesive for the battery cable connections. After shrinking, this stuff is pretty thick and very tough. Most heat-shrink tubing is more like a rubber sleeve, but this is closer to rigid plastic, so it should provide outstanding strain relief for these terminals.
I then slipped a rubber boot over the end. All power leads will have boots for protection.
This was a pain in the ass to slip over the super-thick heat shrink tubing, but it should work fine.