Dustproofing a caravan

G'day all,

We're about to start off on a WA/NT trip which will include a bit of dirt road travel. We have a semi-off road van and, while do not anticipate any extreme off-roading a-la-the-Gall-Boys, we will be doing quite a bit of (hopefully reasonable quality!) dirt.

My question is how to go about sealing the main dust entry areas like the Air Con (we have a Truma A/C with the entry at waist height), the hot water heater (also at waist height) and lower fridge vent. The last trip away was OK from a dust point of view, but I feel that it would be even better if we didn't have to spend ages cleaning everything after each dirt stretch. (A happy wife = a happy trip!!)

A couple of bits of explanation:

* I'm in the process of building a bilge-blower powered filtered-air blower to feed the interior on the move, but feel that it will be far better and more efficient if it has fewer holes letting the air out so it can pressurise the interior better.

* Yes, we have a scupper on the roof and it neatly channels all the dust from passing road trains straight into the van - not a great hit with SWMBO!

* The fridge is 12/240v only - no gas. I've checked with both the installer and another caravan repairer about blocking off the bottom vent while leaving the top one open. Both seem to thing there's no problem here. It certainly doesn't seem to worry the cooling efficiency of the fridge so far.

* We will have a gas alarm installed by the time we leave. Gas is now only used for hot water and cooking.

So, what I'm looking for is any kind of suggestion about how to attach and detach (easily) external covers for the A/C & Hot water for while we're on the move.

Anyone done this before? Velcro, studs, plastic sheet + gaffer tape???

Cheers,
Chris