I think the whole point is to squeeze as much epoxy out as possible to get maximum fibre to resin content. Once the fibers reach their limit of compression no more epoxy can be squeezed out.

I've just made a US base weedy for the other half to use on the estuary, all I had at hand was an anvil and a few boxes of spanners, but even that helps. Must make myself a press.

not sure about fins but lots of hi tech composite structures (eg F1 chassis) are cooked in an autoclave. this allows high temperatures and pressures to be used. pre-impregnated fibres are normally used to give the best resin to fibre ratio.