Click on the image above to see what I've done.
Whilst not waterproofed for serious immersion, I was much more concerned about magnetic or iron based sand infiltrating my skid cover and affecting the signal.
Some people have bagged their coils for use in water although this can have other signal issued if immersed in water surrounded by air and plastic.
I have used my Elliptical coil like this in puddles and in water on the sides of creeks before so it works fine. I think the coil itself is rather well sealed anyway but
unless you use the tape around the dust cover, you'll end up with conductive dust particles which WILL affect your signals.
The BEST reason to apply tape is if you're skimming the ground and smash your coil against a rock a few dozen times, you may eventually (almost certainly)
crack the skid plate. Then your plate will be prone to falling off. On the field, this will annoy you to no end since you don't want to mess up your coil by
not using a skidplate on the same sharp rocks. I was advised to use the tape for these very reasons and I'm extemely pleased with the results. I'm off to the Goldfields with my Elliptical coil in 8 hours and I'm very confident with it set like this.
I used black Duct Tape to create a moisture-tight seal around the cover and the coil. If immersing in water, you should remember to add black (or any color)
silicone to the coil port and where the coil cable enters the flexi-connector. The small gap there is not factory sealed although it can handle light rain to my understanding.
If you need full immersion capabilities, buy the optional 6" DD HF coil which is completely waterproofed up to the connector socket. (BELOW) This is
the best option and was apparently designed for underwater use.