The layout is under a Laserlite roof but is completely open at one end and partially so at the other. The original planning took account of where rain fell, where it only splashed and where the ground stayed dry. I built to the maximum extent in the "dry zone", to within 2mm of the "splash zone", which means that the layout only gets spots of rain when there's a strong wind blowing it in.
Everything used to build and run the layout is exactly as you would use indoors. The only limitations are that I cannot use most card products as they won't withstand damp weather and the attention of slugs and snails; Vollmer embossed sheets are a very honourable exception to this and have proved extremely durable. I also have to keep a regular eye on the woodwork and all the hillsides which are built from newspaper balls under plastercloth; if those get wet there's trouble ahead!
I wouldn't use a domestic vacuum cleaner at any time but do have a small "dust buster" hand-held vacuum which is very useful for lifting leaves and insects from the layout. The Dapol cars are good for collecting fine dust from the track and insect wings often turn up in the collecting tank but not so good as track cleaners. They do work but other methods are better and less abrasive. If you can find a CMX track cleaning car those are the dogs nuts - but as they're also a large brass tank they are heavy and costly to ship and far from cheap to buy.
IPA removes dirt from the rail heads which a vacuum cleaner won't do. It doesn't lift dust and other solids. I use both a vacuum cleaner and the IPA spray for different cleaning functions so recommending one against the other isn't appropriate.
I now have a whole new appreciation for the quality of your workmanship my friend!! I never realised that your highly detailed layout was as exposed to the elements as you have just described.
It diminishes the excuses I have been making about my own layout, which is located in an un-lined Colorbond shed. When the rain comes in from a particular direction, I can suffer the same fate as you, with certain sections of the layout copping a drenching. This is one of the reasons I have not done any scenery to date.
Dust is my constant enemy and I can vouch for the worth of the CMX tank wagons, of which I own two.
I fill them with IPA (I bought 4 litres of the stuff off ebay a couple of years ago and still have about 3.5 litres).
If the layout has been standing idle for more than a week, I tend to push the tanks around the layout with a pair of double headed mainline locos (usually 2x Austrains 80 class, as they are my least expensive locos). The CMX tankers are very heavy and need 2 locos in my opinion.
Once the track has been cleaned with the tank in front of the locos, I then add the CMX behind the 2nd loco and add a reasonably short train to do some more laps around the main lines.....one in each direction.
The five-fingered-shunter is used to push/pull the CMX into sidings if/when I think I'll need to drive a loco in; otherwise the sidings are not cleaned very often.
I also use the "dust-buster" idea (mine is an 18v Makita) to suck-up the larger stuff, including the ever-present mouse poop from the plague we have been having here for a few months now (but they're just about stuffed now that the colder weather is here).
Cheers and thanks for sharing your video...
PS: There is one on ebay at present for a reasonable starting price:http://www.ebay.com.au/itm/CMX-HO-unpainted-Brass-track-cleaner-/131205627492?pt=AU_Toys_Hobbies_Model_Railways&hash=item1e8c76fe64&_uhb=1