You've answered your own question I think although with a filly laden camper, you may need a little more pressure than standard. In wintry conditions I'd keep them at the spec pressures and no more but most tyres also have a maximum pressure displayed on them too.
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Your van will weigh in at over two tons when laden, having sloppy under inflated tyres will wear them out unevenly,, petrol consumption will increase and cornering will get "interesting if you need to turn sharpiish.
The tyres are "commercial" not car tyres, much more reinforcement and plys they are designed to carry heavy loads and not get out of shape, the correct pressures will ensure they do the job
Just bear in mind what I said regarding maximum pressures for the tyres themselves - it will be written on them. 55 sure is high. Most I've ever gone is 48 on the rear and that is probably excessive in the winter.
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