Yeah, definitely use a high wattage soldering iron when soldering leads to Deans. It needs to be done fairly quickly. I use metal alligator clips on the contact terminal side as heatsink while it also holds the connector in place.

I use something like this + a small c-clamp to hold the apparatus on my workbench. Search 'helping hand' on Amazon.

https://images-na.ssl-images-amazon....8L._SX425_.jpg