Electrical tape will be pretty stiff. I recommend getting some teflon tape. Commonly used by plumbers to seal pipe connections. I use it to seal anything that I make that has a shield. It is also very handy to keep wires and sleeving in place without using adhesives since it seals with itself. Pretty damn cheap too.
http://www.homedepot.com/h_d1/N-5yc1v/R-202206819/h_d2/ProductDisplay?catalogId=1&langId=-1&keyword=Teflon+tape&storeId=10051#.UJGapsWHIm4
http://www.homedepot.com/h_d1/N-5yc1v/R-202206819/h_d2/ProductDisplay?catalogId=1&langId=-1&keyword=Teflon+tape&storeId=10051#.UJGapsWHIm4