I don't think anyone is saying that the pool can't be done. But it does seem clear that it is problematic, and could not really be a must have.
On the question of advertising. Even for a limited poster/flyer campaign, that can cost a bit and it is very indiscriminate.
Local radio and local rags are usually desperate for stories. If you can get them to do a story before the event, and not reporting on it after the fact, that can help and is free. You need to create a story about the club, provide photos/photo ops, to be a story as lead in to the upcoming show. Most journalists are too busy and making instant content for them also helps. If local newspapers have comments section, you can also create chatter about a local show among club members, e.g. someone posts a bogus question like, 'Does anyone know of any local boat clubs or shows this summer?', to start the chatter.
We can also be our worst enemies, even on this forum. There was someone who used to really push a local show, with all vigour. Result, some people used to complain about it.
I also think that there are many more opportunities to cross pollinate with other branches of modelling. There may not be a model boat show in the south, but I would bet that there are other model shows; some of whom would welcome the extra variety. Some of the traders also have a obvious crossover that would build their business (3D printing, resin casting, figures, electronic components, etc.). We have many members on here who do other kinds of modelling, perhaps they know more of the show scene for their other disciplines.
I don't have time to follow other model forums, but RCGroups caters to all kinds of models. Other sites may be promoting other kinds of model shows, it may be worth contacting the organisers of those shows. This could even be done by individual model boat clubs. Basically, any exposure of model boats to a wider audience, especially other modellers, can only be good.