CARAVAN BED GAS STRUTS

The general rule of thumb is 20% of the lid length from the hinge,
1000mm length = 200mm from the hinge.

You'll need to know the weight of the bed too, Danny, as you lift it up, so you can work out the Newtons of strut required. Also decide how high you would like the bed, for access, to get the length of strut too.

Ovesco have a good range of struts, and their service is excellent. No affiliation etc.

Bob

this might help
choosing the correct strut

Go and do some tyre kicking around the van yards. Take a tape, pencil and and paper in your pocket. Take note of the strut(s) used and measure their locations. This way you will be able to see how others have done it.