Diodes+H2O

shrink tubing over the diodes as far as the insulated wire with some silicon grease inside as well that is extruded as you shrink the tubing. That leaves zero space. Of course a long conductive path can be formed with other parts and enough water.

Another option would be to buy some hermetic shrink tubing. There are several manufacturers out there who make shrink tubing that is lined on the inside with a layer of heat activated, waterproof adhesive. When the tubing is shrunk, the glue melts and seals the contents inside. There is enough adhesive inside to actually ooze out both ends when shrunk. Great stuff. Not cheap, but great.

di electric silicon jelly, google search that.. also double mechanical seal j box and seal after wards with same jelly too, avoid condensation provide dry ait circulation thru conduit if poss, or j tube. 1 airchange per 4 hrs, not much needed, but it makes all the difference in long life. J Bo

If it can be truly seales with silicone inplace gaskets and silicone into all conduit feeds a small bad of silica gel dessicant would also work. It will not work for long if air can get in and saturate the gel over time

Earlier thread in this forum addressed a similar situation. One guy said he used pvc pipe with pvc end caps with holes drilled in them. Run the wires through the holes in the caps and encase everything you desire inside the pvc pipe. Then fill the pipe and caps with silicon and press everything together. I noticed a patent on a similar setup but not sure where I found the patent now. Never tried it but it sounds good.

Most of the friends suggested Silicon-grease which is quite valid, as you know even EHT devices are moister & arc-over protected by it.

Shrinkable sleave or other solutions may hinder the cooling of diodes if those are power diodes

There is a caulking product called NP1 which will last forever. You just need to not cause a heat problem. And once it sets you probobly are stuck with it. Or try Epoxy.

Use a type 6P JB and fittings

it is for shipborn use, and is submersable to 20 feet of water

GE (General Electric) makes an electronic grade RTV (Grey RTV 167) that would do the job great. We use it in all kinds of military applications to prevent moisture and vibrations (from breaking the solder joints). Dow Corning also makes an equivalent but I don't have the part number on hand...

I confirm it for Industrial use. A leaflet is with all packing & the best for the job may be selected & ordered from the Vendor.

There are many vendors who supply RTV Silicon in tubes & tin for bulk use.

You want to get really hard core about it?

get yourself some 2 part epoxy and fill the box your diodes are in. down side is that you will NEVER EVER get them out, if you burn one up you make a new box with new diodes. absolutly water tight though.