You cant check your oil if your van is not on the level.So how do you find out if your van is level and your on holiday without a spirit level ,easy use a round fruit.place it on the floor to see if it rolls ,oranges would work ,but I found plums worked quite well.just don't tell anyone what your doing
Do what I do,Check the oil on the flat when you get there, dig up the soil from under the van when you've finished camping, extract the oil from the soil, measure amount and top up, easy really
Personally I prefer to use an olive which can then be added to the martini the missus will be making me.