Heltec V2 and V3 Meshtastic Lora case: Fix for heat set inserts

Added a few millimeters of blocking to screw holes so inserts don't fail to set (original model would tear through the sides).  Still, you should be gentle screwing / unscrewing, as these are still very delicate.   

I only recommend putting inserts in the 4 corners for the backplate.  I have not tested the other 4 slots.

The antenna hole will fit perfectly with the standard heltec antenna connector, but it may not fit for after-market parts.  Measure first if using aftermarket antenna connector.

Parts used:
- M2x8mm screws (Much too long, but they're the shortest I have)
- M2x3x3.2mm heat set inserts

Added a few millimeters of blocking to screw holes so inserts don't fail to set (original model would tear through the sides).