Thanks, these are all great ideas. We are also thinking of cheaply "jacking" it, and using any old non waterproof connector, and shoving a small thin plastic "tube" over it when connected. and then having kind of jubilee clips pull tight at each cable entry end of the connector, so as to pull the plastic so it seals around the cable and connector, giving an element of waterproof-ness
Being super-cheap, we are even thinking of a bit of choc block, wire into each screw clamp, tie a knot in the wires as they go into the choc block, then a small plastic bag around this, then elastic band or jubilee-clip round this for water proofing.