If the van is 20 years old just check that the tyres are correct for that size of van and loading unless you are certain that they are right. Each tyre should be marked with its loading capacity and then its normal pressure. Look here for the detail
Phil
------------- If you're not on a fell your wasting your feet and for 2014 it's.......Feb Castleton Mar North Yors Moors; Apr Sutton on Sea; May Thirsk; Jun Clapham/Riverside (Lakes); July Wharfedale; August Crakehall; Sept Knaresborough; Oct Wirral Park/Clitheroe
I towed my `90 Daystar (1100kg) on 175/13 tyres. Wasn`t sure of the pressure required. There was 38psi on both wheels and they ran a tad warm. I put in 44psi (max for tyres is 66psi) and they ran cool. So 44psi it is!
------------- Peripheral people don`t have as much excitement but they sure live longer
Check the rise in tyre pressure between cold and warm next time you get a chance. It should be about 4psi after running at motorway speeds for an hour. If the change is more than 4psi, you need to increase the pressures a bit (and lower it if less than 4psi).
Once you've done that, the caravan tyre pressures are correct for the actual loading of the van. Google "4psi rule" for more info. While you are at it, you could check the towcar rears, so you know how much to increase the pressure when towing.