Following a friend's advice earlier (and having watched this youtube instruction film), I have this afternoon been soldering EC3 connections, which seem pretty solid.
One thing I did slightly differently was rest the tubes in a hole in a piece of wood instead of holding them in pliars, as the latter would tend to act as a heat sink.
I have connected the female plug to the battery using standard spade connectors, which will be wire-locked (permanently).
This is a work in progress, but the intention is to have a plug-in board (below) for jump starting from a battery booster. This could also be used for charging the battery using crocodile clips. But I'd prefer to plug a male EC3 with a Tamiya/Kyosho socket on the end into the battery one, connecting it to the charger that way.
The board (wood because it doesn't conduct) has steel bolts secured through it and wires clamped in place (see crude drawing). Each pair of wires will have an EC3 plug (a male one to connect to the battery's female; a female to connect to the engine EC3). This provides something really solid for booster jump leads to grab on to. It is crudely drawn but will be tidily constructed. (HTML problems, so can't shrink this bit of text!)