Levelling ramps are your first and cheapest option, as you say it might just be the fact you are off level.
But as said above, it might also be the movement of the van on its suspension as you and others move about, there was someone on the forum a while ago who was considering selling as they couldn't cope with the movement.
If levelling doesn't work, then speak to
@CRS Performance to see if they can stiffen it up (cue
@JOG , apologies in advance
@CAMPA !). It is the more expensive fix but shouldn't be wasted money if all the other happy customers of CRS are correct.
But
@Bav has a good point, if it is a new conversion there may be glue / carpet or other fumes that are affecting you.
If none of those work, sell the van, buy a motorhome, install self-levelling jacks!!!