Teflon dielectric connectors are not hermetic, so you are not going to be able to make one so after the fact.  A standard trick is to smear some RTV on the flange before mounting and inside of the cup, trying to keep the centercontact metal dry.  

A better trick would be to go with a hermetic N connector that employs a glass to metal seal, probably the glass seal soldered into the case with a field replaceable N.

In connectors that you just want to keep clean from high power arc over, you can fill with a dielectric paste.

As biff44 pointed out, hermetically sealed N connectors of the bulkhead or panel type are available from a number of sources. A quick check of Pasternack shows a PE4137 N female with solder cup (www.pasternack.com).

Another possiblity would be a dielectric grease which many field technicians apply inside the connector to keep moisture out. Check out Silchem (www.silchemmarketing.com).

But is that what you're protecting against in the desert?

TTFN

I have the Pasternack connectors already. They are just teflon inserts. Co-workers are concerned with the Teflon either oozing out, or becoming loose and moisture propagating through to the cable and affecting cable loss and corrosion.
Glass captivated center conductors are hermetic sealed and I believe would be better. Our cables have a moisture seal in them.
kch

Now you are confusing me!  The "bulkhead mounted connector" on the housing has NOTHING to do with moisture leaking into the cable that attaches to it.  You can use one made from bubblegum, for all the good it will do you.  You have to use a hermetic mating connector ON THE CABLE if you want no moisture to leak into the cable.

You had better explain more about what you are doing.  Sealing up your cable will just trap any outgassing from the cable materials, and probably make things worse.  Cell phone tower designers use desicators or nitrogen positive pressure systems to keep water out of their high power feeds.

Higgler-
I would recheck what part number Pasternack connectors you have. I have some of these PE4137 connectors I bought 2 years ago. They have no teflon - just a grey/green glass through which the center pin/solder cup passes.

I purchased pasternack PE4013 and PE44077 bulkhead connectors, they are N-f bulkhead mounts. The solder pot center pin is captivated with Teflon only. We are using it in an enclosure that is not fully sealed to the environment.

OK, I feel really silly now. Comcokid, the part number you referred to is what I was looking for.
Correction, I feel silly, but quite good.
Thanks Comcokid,
Kevin
biff44, I believe that if you connect cable with an N male connector to an N female panel mount who's center conductor is captivated by a leaky Teflon (suppose the Teflon was perforated, or just cracked), then moisture, salt and small bugs, etc. pass through this N-female into the Teflon mating surface between the two connectors. We are making an antenna for high power radar testing. Crap on that interface isn't good and only Noah likes an Arc while he's working. The normal environmental seal between N-m and N-f bulkhead connector is only good if the N-f bulkhead is sealed well, i.e. hermetically sealed, and the moisture seal/oring in the N-m works well. I was fine with the standard Teflon, and planned to conformal coat and captivate it, but co-workers wanted a higher level of protection, hence the hermetic need.

FYI - the PE4137 center pin is silver plate, not gold plate like many other N.

An additional method of sealing is to get some glue-lined heatshrink such as Daburn SM278-1" to shrink over the completed connection (available from Digikey).

If it were my project, I would just fill the connector's insides with dielectric goop and be done with it.  My biggest concern would be dust collecting on the insides and causing carbon arcing.  The dielectric paste will prevent that.

Is silver plating that much worse for corrosion? Our environment will see more heat cycling than moisture or salt problems.

The hermetically sealed approach was a request/demand. I am actually comfortable with just gooping the present Teflon puppies.
T hermetically sealed PE4137 connectors are only $8 each, which is nice. Maybe I'll have them gold plated if needed, or find some others that are already gold plated. Maybe add some dielectric goop and heatshrink too.

thanks all for the info,
kch

Gold doesn't corrode and protects the base metal underneath better in high-moisture environments. I think silver is fine for your application which sounds hot and dry. Tarnished silver (silver oxide) still conducts. I believe this is just a matter of preference.