Using the proper wire nut and taping it to the wire once it has been twisted properly should remain serviceable without any problems however if you really want to do it right, there is a crimp connector that looks like a top hat where you insert both wires in one end and then crimp the other end and everything is contained inside the connector. The connectors are semi transparent with a copper crimp ring inside. Go to the Home Depot or Lowes and look for them in the electrical department. (See Site Below)
Note: If you use in a damp location, it is advisable to fill the wire nut and/or top hat crimp with a dialectic grease first (B4) you twist tight and/or crimp. This keeps the elements from reaching the bare wires inside.
The rule for crimping is:
Crimp once. You never make a second crimp because the second crimp may loosen up the first crimp.
The BEST crimp tool is a Ratcheting Crimping Tool, one that must be squeezed all the way down before it will release. (See Site Below)
Because using a cheep tool that does not ratchet may not crimp all the way and you may loosen your grip and the tool may move and you wind up with a less than perfect crimp.
The Crimp Tool
The Crimp Connector: