Crimp-on wire connectors work well if they’re crimped properly (a 5/16-in.-wide crimp) and sealed (usually with heat-shrinkable tubing). But most cheap crimping tools only make a 1/8-in. crimp, so you’d have to make four of them for a simple butt connection.
Invest about $25 in a professional crimping tool (OTC No. 4497 from www.sjdiscounttools.com). Then buy a roll of electrical moisture sealant (3M No. 06147; about $20 from amazon.com). Then just follow the steps in Photos 1, 2 and 3.