FIRST, duct tape ain't what it used to be...if you tried wrapping some splices with "real" duct tape you would get a small fireworks show...but regardless forget about using something non-electrical to cover your splices.
SECOND, where are these splices that you can just leave them uninsulated ?
and C, if you don't have either glass cloth or cambric , try wrappng them first with vinyl but wrap it with the sticky side out, then rubber or 130C , then more vinyl, but this time wrap it the regular way...and don't forget to twist the tail so the next gal, or guy doesn't have to use an electron microsocope to find the end....
BTW ....when you are assembling your splice, do you whack the bolt and re-tighten... after... you have snugged it up ????