Re: Low buck projects- Let's see 'em!
There are all sorts of different systems available to create waterproof electrical connections, both for 12V DC and 240V AC. I've come across "potting compounds". These are cross linking polymers that are normally used to create waterproof insulation for cables underground or outdoors. You mix equal amounts of two liquids, stir and within a few minutes it will set, creating a removable insulator that does not allow water to penetrate at all (IP68 rating). I've used all sorts of boxes to contain my connections and temporarily press butyl tlape around the cable exits to not allow the liquid to run out before it sets. It can easily be scraped (or spooned) out. There are some that can be reused, some have to be discarded after taking it apart. Here in the UK I've used Magic Gel by Raytech. I bought 2 liters from fleebay at a fraction of the normal cost - this will last for a few boats to come; it has no shelf life. 3M used to sell a similar product in North America and I am sure there are others available from more manufacturers.
Here's the connection box for my bilge pump as an example (without lid):
Raytech Magic Gel in bottles | Rapid Online
Yet my heart hammers now, yearning anew
wanting the steep salt-water road
longing with lust to roam rough seas, alone
to seek out some far foreign shore
From "The Seafarer", an Anglo-Saxon 10th century manuscript.