Hello iuliu76, I think that silicone is the answer to your problem. I
have used RTV silicone before and it is a very good product for your
application. Here is some good information:
RTV162 White, one part, high strength, low odor, non-corrosive neutral
cure, electronic grade silicone adhesive sealant. Meets Mil spec
requirements and UL recognition.
Product with good flow properties, low shrinkage, excellent tensile
and tearing strength. Used wherever high mechanical demands have to be
met, e. g. cable end terminals, connectors, moulds, etc.
This might be the best choice for "molding some watertight connectors".
I found some very interesting info on silicones on this page.
I believe this will be the solution for you, Redhoss