So we just hung some photos and bits in our 'van.
We used some plasplugs and it seems fairly strong. A couple of them bottomed out a tad, we don't think on the external skin but maybe on some bracing.
For the heavier pictures we actually found the wooden supporting struts behind the wall. They can be located by looking for the screws on the outside of the van. We actually just pushed the wall until it didn't wobble and was firm. Done the trick for us.
Linkback: https://staticforum.co.uk/index.php/topic,757.msg1998.html#msg1998