Ron, starting to sort through the thread links in the coil sticky for waterproof plugs to see what the particulars of those are, so I'll let you know what I find out.
One idea though, that waterproof plug from Doc looks to still plug into your coil connector on your land rig so that's probably what you are looking for, but it's pricey. So here's another idea...You could get one of the cheaper waterproof plug setups Excal guys use for swapping coils that don't mate with the standard connector on your control box on your Sovereign, but then wire up a male/female patch for that plug to a short length of coil cable, with a standard coil plug on the other end of it. That way you could plug your modified coil plugs into that cable and then the other end into the control box on the Sovereign.
That would save money over Doc's, but then again you are back to the old problem of now having all your coil plugs changed over to something new that can't plug directly into the control box on your land rig, so not only do you have to change all the plugs on your coils over to that, but you'd also have to change any coil back to a standard plug if you ever re-sold it, unless of course you supplied the buyer with the mini conversion cable to adapt the coil to a standard control box plug. For that reason Doc's is still more attractive even at the much higher price than other waterproof plugs that won't mate with the control box without making an adaptor cable.
I'm still digging through those threads and on the net to see what is out there. Two things I'm trying to dig up- Some kind of waterproofing grommet that will just slide over a standard plug and make it waterproof, and also a setup like Doc's where the waterproof plug will still mate with the standard control box connector, yet becomes waterproof when mated to it's other half on your water rig. Some kind of grommet deal though that just slides over stock plugs would seem to me to be the most attractive solution, because it wouldn't require changing plugs on coils, even though a plug like doc's will still mate with the control box you still have to change the plug on the coil with that setup.