I have both the liquid tape and 3m self fusing silicone tape
http://www.amazon.com/Scotch-Self-Fusing-Silicone-Rubber-Electrical/dp/B0029Z5RSYThis one is heavier, I buy it in ten foot roll at home depot about $13
The thick tape will be a more permanent solution, you will have to cut it off with a sharp knife if you ever need to get to the connection,
But absolutely nothing will get in there if you use this stuff correctly
Stretch it about 50% when wrapping the connection
No need to cover it with anything else
This is high voltage, high current, weather proof