I was looking in Model boats and Marine Modelling International in the newsagent this afternoon (there's a model of a paddle steam launch in MB but I didn't read the whole article) and I just found out there's a Grays Thurrock Model Boat Club! All these 20-odd years living here and I'd never even heard of it!
Unfortunately, it's in Belhus Country Park (which means nothing if you're not from around here) and as far as I know, is only accessible by car.
So, it's still easier for me to get to Southend (train to southend east, short walk to the park) or Bluewater (regular buses going all the way there)