Awnings and rain.

1. Are they at all effective in keeping the dew at bay when sleeping just on a mattress on the ground?

They certainly are.

2. How effective do people find them in rain? The gap between the roof of the vehicle and the awning bag must be an issue?

Depends how far out or in they are fitted (mine sits approx 50mm in from the gutter) and which way the wind is blowing. I made a homemade curtain wall out of plastic tarps from bunnings, works fantastic and only a fraction of the cost of a genuine awning wall.

Do not store any awning fabric wet...............mould will eat the canvas.
Use clips on the end of tie down rope to secure to aluminium rail, its just easier.
Awnings won't come with "sand pegs", large sand pegs a a must.

Yes Nats, they are great for dew and rain, but . . .

For rain, you MUST angle it pretty heavily down, as they will stretch with the wetting, and can end up like a balloon in the morning (if you're lucky and it doesn't split down the middle !).

A 2.5m x 2.5m won't cover you well at the ends, with a little wind etc and light rain.
For a Patrol, I would go the standard 3.0 long x 2.5 out, and you can get the clip in tent, like this one . . . Ebay awning tent

Even with the clip in tent, ALWAYS angle that roof down if rain is possible.
It would be a very rude awakening if a ballooned awning split and dumped (I dunno) maybe 40lt of icy cold water on you one morn !!

The gap between leading edge on vehicle roof isn't a big issue normally, maybe if blowing from that way, but I just throw my swag under there, either on the ground or on a stretcher if I feel like taking it.

You can pack them up wet (what choice do you have ?) as long as you open it up when it clears (lunch time, next camp, or at home) and dry it out thoroughly.
They dry fast, esp a little wind and sun.

Always guy it down, I have had one blow over on me, no damage, but a worry if the slightest breeze is blowing.
Me, I don't have the lines out to trip over, but do a couple of half hitches down the 2 poles, and then peg hard down near the pole base.
Sand bags similarly placed for at the beach works well, as you can just take them empty and fill there to weigh down :)

Nats

Mainly use my awning for sun protection , but its does come in handy in the rain .
That all depends on the wind strength and angle of the rain.
Certainly helps with the dew and condensation , as we leave our chairs and table out most nights when we camp.
I just use a silver tarp I made up to fit my troopie.

Cheers

I got 2 supa peg ali poles, cut to length, and mounted under the roof rack to align with the ring on the duraig tarp. The poles slide out about 800mm on the drivers side, hook on tarp and pull over the rack, set up 4 poles and I have 6mx6m cover, got some oztrail sidewalls on sale for $28 each, shade cloth down and thats the living and sleeping area. If I want to take the 80 out I just put 1 pole on drivers side, retract rack poles and drive out, seriously it takes no more than 15mins to set up. Also ahave another pole that goes in the passenger side rear, hook on tarp, adjust till tarp is tight and put up 2 poles, gives me 3mx3m over the rear doors. So 2 options and very little time to set up, have used this for the last 2 years with know probs. Was set up when it decided to pour down, mate had a foxwing and found water coming in between the roof and the foxwing, ended up spending the day under ours.

Rain is not the issue,wind is though. My mates A.R.B. awning got shredded at Salt Creek,a few months ago,but my ghetto tarp stood the test. Wind was around 60 to 70 KPH.

I have an Ostrich Wing which would have to be one of the strongest around. It is quick and easy to set up and close up. Even though they say you don't need to I always pole and peg it when open.

It does have some issues like rain/water coming in between the awning and vehicle roof, water including a heavy dew will pool on the topside whislt the underside will attract condensation which will run to the low sections and drip on to you. I brought these issues to the attention of the Perth supplier at one of the camping shows, they quickly took me aside away from potential customers and advised me "they are for shade only".