I've always put a layer of tape first since my first DIY install, only because when you go in later to remove the connections, you will have to use a hammer and chisel to remove the Coax Seal after a season or two in the outdoors. Ugh.
I can suggest the Diamond D130NJ discone, as I have had great results with it. I have it on outside mast 25ft high on side of house and I put it thru 8-port Stridsberg multi-coupler and feed several scanners with it. I have a coax feed that I alternate with SDS100, TRX-1, and BC125AT and it works great.
I just bought the Diamond D-130NJ from Gigaparts about an hour ago. Do you mind telling me what coax you are using. I am going to purchase the coax with both ends N type and a jumper N type female to BNC male.
I've had my D130J (with PL259/SO239) up 50' for about 11 years now and it's still up there performing as new. Absolutely impervious to any wind/weather/ocean air. And its performance is to me satisfactory. Now that I run my R8600 to it for VHF/UHF it's even more impressive on that rig than the BC785D. I feel, as the other guys have said, this is THE antenna to have.
Far as coax, I swear by Times LMR240 hardline. Right-sized diameter-wise and lasts forever. I have a run of the LMR240 flex on my HF loop but to me the outer jacket is questionable.
That could be one way to do it but the professional antenna installers I've seen, and also how I do it, are to first put the rubber mould or vulcanising tape on first, to make it water tight, and the electrical tape on top of that to protect it from the enviroment and animals. Haven't really seen that first layer of electrical tape being applied, neither in real life or in instructions that comes with an antenna connector sealing kit or in videos.
As PRC said, it aids in removal. Putting down the half lap and back of electrical tape protects the connector from the sealant. When you put the sealant tape over, you extend beyond the first wrap of tape. Then you put the last layer of tape over all that, extending beyond the sealing tape by a bit.
You can certainly skip the first wrap of tape, likely won't impact the waterproof-ness of it all. But when it comes time to remove everything, it's a lot more difficult.
For sure it will be much easier when you later need to access the connector, but electrical tape isn't flexible enough to make a tight fit and leaves air pockets that with time will collect condensation moist. The purpose of that vulcanisation tape or that play-doh type of mold are to make absolute contact with the metal and having electrical tape as an inner layer seems contra productive. Why then not use only electrical tape and then seal just the ends with vulc tape or mold? I must have opened hundreds of 7/16 and N connectors made by both 2-way antenna and cellular installers and never seen an inner layer of electrical tape. Actually some cellular installers doesn't insulate at all as they say it traps moist and it's better to leave the connector open to the enviroment, if the connector are designed for it. Maybe it's down to what region you are in, US or Europe.
The connectors all have some void space in them, so if condensation is somehow going to form, it's got plenty of places to do it. Same with air core cable, the hollow center conductor of 7/8 and 1-5/8 Heliax, etc. The goal is to keep water out, not provide an air free connection.
The antenna farm is a reputable company. I've used them for small quantity purchases at work that fall under the minimum orders of the bigger companies. They usually have what I need in stock and ship it quickly.
I ordered a 50 foot cable assembly of Times-Microwave LMR-400 from MPD Digital with N type connectors on both ends and a jumper RG8X BNC male to N female. Now all I have to do is to wait for the weather to get a little warmer so I can put everything up. Thank you for all of your help.