That guy in the video does it the right way -- Crimp, Solder, Seal (Heatshrink). ALWAYS do that for ALL automotive wiring - inside or outside. Those little butt connectors are cheap if you buy them in bulk. Check out Waytek, Del City, or Mouser for pricing. Its not that expensive. If you front the $30-50 up front cost, you'll have a lifetime supply of connectors and will always have them ready. I'm doing installs off of stuff I bought seven years ago. Buy the good double-wall heatshrink too. I hate it when I see folks doing the classic "Western Union Twist", then slap some Harbor Freight brand electrical tape and call it a day. Then they complain that their crap doesn't work all the time or that they see sparks. Corrosion is your enemy inside or outside for wiring.