I would use wire nuts that have a brass insert with a set screw that you
tighten onto the wires, after trimming the excess hanging out the insert
you
screw on a plastic cap. When finished it looks just like a twist-on wire
nut. A "Marr #2 insulated wire connector" is listed as good for two solid
or
stranded #10 wires down to five #14s.

I was all set to sold the wires, but these look like they ought to be plenty
secure; if anyone locally has them. Thanks