Only a tiny fraction of fleas actually live on cats and dogs- the vast majority are present in the ground. And yes, they can live between floorboards, depending on the width of the gaps between the boards (if fairly wide, the eggs may fall through to the ground beneath, but if the boards are 'touching' (i.e. verynarrow gap between) the flea eggs and larvae can live in there.
As to the enviornment.. I'm not sure whether you can get insecticides, such as insect growth regulators in a spray form to spray the problematic areas as required. You could consider asking your local landscaping supply or even local produce store as they may have some ideas.
The best product out at the moment for fleas on dogs is comfortis (and I do believe that from the start of next year they're going to try and get this registered for cats aswell), or panoramis- panoramis is a new tablet (only just became available) with the same ingredient as comfortis, in addition to milbemycin which also controls intestinal parasites and heartworm- so the one once monthly tablet does fleas, heartworm and intestinal worms (except for tapeworms- praziquantal is required if these are a problem. However, the main tapeworm in dogs is Dipylidium caninum which is transmitted by ingesting the 'carrier' which are fleas. So, by superb control of fleas, the risk of these is reduced. If a dog eats frogs, geckos etc they can pick up Spirometra tapeworms as well which need an even larger dose of praziquantal to kill). Panoramis is actually slightly cheaper than sentinel, which is a similar product that does fleas, heartworm and intestinalworms, however sentinel is only a growth regulator- stops adult fleas from breeding, it doesnt kill them. Anyway sorry for going a bit off topic. I hope you can get a handle on the infestation, they're horrid to deal with.
If you used something like comfortis or panoramis, one thing you could then try is walking your dog through your problem areas- the motion, heat, 'scent' of the dog will be detected and trigger hatching of eggs, development of larvae and fleas jumping on the dog. However, because panoramis and comfortis are so effective- they will kill the fleas very, very promptly. Or even just walk through there every now and then to trigger eggs to hatch etc and then treat with environmental treatments (insecticides for example) - it'll generally make them more susceptible once they're out of the eggs.
Something else too- Warm, moist conditions = superb for fleas! So they'll only get worse through the wet season and with the lovely warmth we get. However there is a limit to this- if it gets too hot (happens occ. in QLD. depends on where you are) you can get reduced flea numbers again because its too hot for them.
Its best to get control of them ASAP to drop their numbers now- otherwise they will exponentially increase in numbers as the environment changes to their favour at this time of year!