Have you tried any of the waterproof wirenuts that come with a sealing compound in them? Our UST sensors come with a 2 part epoxy kit. We mix, snip one end, stick the wire nutted connections in, and cable tie around the base. It hardens rubbery so it can be cut into later. If you check the terminals catalog at www.terminalsupplyco.com
, you will find several adhesive lined shrink and other insulated connections.