My van came out of hibernation last week. After a clean I noticed the pop top mechanism was stiff. I think the correct stuff is the white Lithium grease as Pepe has posted, I know it is usually used on car door hinges etc. I did not have any so used a dab of Vaseline in the horizontal grooves of the hinge. It appears to have worked nicely.

On other hinges, slides etc eg window stays, I use a ptfe spay. This is a dry lubricant so dirt cannot stick to it and turn into a grinding paste.

Colin