Load rating of your tyre is 97 = 730Kg per tyre at 65psi (check the age of them, 5/7 years max depending on peoples views) even tyres with lots of tread can be an accident waiting to happen as the rubber perishes.
I have a version (dealer special) of the same 1991 Elddis Wisp called a Vogue SL. It took me a while to find out the correct tyre pressure. Alex has it right at 52psi, although I usually inflate to 55psi.
------------- The Sun always shines on TV.(and not on my caravan!)