No crimp on any terminal (let alone an insulated terminal) will crush the wires to the point where there can be no ingress of a liquid!
I have a little experience in doing submersible well pumps and cables
. All of these are butt spliced at the pump so we are talking at least 60 feet if not 150 feet below the water
line. I have spliced up to 480volt connections with the following method and never had a failure, even in hot salty mineral water
Un-insulated butts (always use solid barrels, no split barrels, hand crimped with the trusty old T&B’s on smaller wire, a coat of Scotchkote not quite allowed to dry and then wrapped with Super 33 Plus. This includes taping the crotch of drop cable with a sheath to prevent ingress of water under the sheath. About 4 complete passes over the bulk of the splice with 50% elongation and 50% overlap. If it needed additional mechanical protection, as in a rough well casing, then an outer rap or two of 130C.
I have pulled a severed 480 volt mine cable out of the drainage ditch when a mucker cut it with the bucket and put it back into service
in a few minutes with the same technique and the same results; done properly a taped joint will not fail!
There are some cases when self-fusing tape is better but seldom needed for most applications. Either Super 33 Plus or Super 88 Plus will fuse to itself if it is properly stretched (technical term: 50% Elongation).
What delmarray showed in his post is not a substitute for Scotchkote! I don’t know of any sealant that has a UL stamp other than Sckotchkote. I have tried some of the other, including Starbright and find it to be almost worthless in sealing.
On marine connections I don’t use ANY insulated terminals, as I don’t think they crimp uniformly when you try to crimp the plastic. You don’t have any arc
potential anyway with 12 or 24 volts. I crimp with the T&B’s, (a non-insulated type of crimp, mostly), use some anti-oxidant (kool-aid) if non-tinned wire. Encapsulate with Scotchkote and cover with regular heat shrink (in this case the heat shrink is simply a mechanical protection for the Scotchkote).
Tinned or not tinned: Use tinned wire in most cases, as it is just added protection and the make-up less exacting. In case of big runs of long cable (anchor winches come to mind) use MTW or even THHN. If the ends are subject to moisture or need be changed out often for some reason then butt splice a nice whip of tinned wire to the end of the run. Saves big bucks and lasts forever.
Use no sealant with acetic acid around copper!
Even if you can use the crimped connection for a dog leash or to pull the Queen Mary behind your sloop
, don't! It is an electrical connection not a tow rope!
Dielectric grease or kool-aid? I prefer kool-aid but anything to prevent that does not corrode and prevents ingress of moisture. Keep it clean on the outside if you use Scotchkote over all. Strain reliefs, drip loops, all good ideas. A few good tools, the right parts
and some common sense.