What are few things that could impact your EV range on long trips
1) Weather can be a big factor. For days that are extremely hot or cold you'll be running the AC or Heater respectively and that could be a big drain on the battery
2) And this could get unexpectedly get worse if you are stuck in a traffic jam since you are not able to gain much distance while draining battery to AC or Heather
3) Rain can also lead to faster battery drain where you'll need to run the defogger as well as windshield wipers. 
4) Additional load. If you are planning on taking heavy load like camping equipment, bicycles  it drains the battery faster.