Our geese are out like this - they look for places to hide to nest, much the same as free range chickens would. You could encourage them by having nice soft hay (instead of straw) somewhere where there is semi-shelter. Our geese have nested in the same places the past 2 years - one under a bizarre house we inherited made of straw bales - she just pecked out a lot of the straw and made a nest in the (large) gap between the underside of the house and the ground. The other made a nest from soft dried grass she gathered into the centre of a prickly gorse bush. Both nests gave hatchlings successfully. I think they need the following for it to be a success:
Access to soft bedding and plenty of it - they will cover their eggs when they come off for a break
Semi-cover - so they can see who and what's around, but they feel they can't be seen (foliage)
Reasonably near a food source - don't put food near them, this attracts vermin and other birds, but they won't want to go too far from their precious eggs
Perhaps a choice of places at different levels - one at ground level, one a little higher (but not too high, they are a bit clumsy footed)
We do pen ours once the goslings are hatched so that they don't haul them all over the place, goslings legs are quite weak so it's best if they have a smaller zone to live in for the first 2 weeks.
Car tyres and hay may be good, but I'd try ones without the tyres too - just get lots of branches and foliage around them for a good den. If you do it now they will be starting to look for nesting sites in about a month and they need to know the site they pick is permanent and part of the landscape.
Exciting, let us know how you do