I know this sounds crazy but very recently I had the same problem with the same bolt, where after loading camping gear on shelf it collapsed without warning.
After returning home I didn’t have a clue where to start.
Contacted local VW garage !? Who suggested ( not kidding ) we may have someone with small hands, who may be able to put the screw back in but it could take a considerable time to do this,if that fails then we need to take out the kitchen and other various parts !? I asked him can we not access the cavity from where the spare. Battery is situated, replied No that can’t be done..
Following day went out to the van removed the shelf ( phew )
removed the cover from the battery cupboard took my torch and shone it along the cavity and with a twisted view I spotted the screw lying a few feet along on the floor,
I returned to the house asked my wife if we had an old style wire hanger, removed the hook and cut a length of the wire pulled screw out alongside the battery, so had both bits , then thought ok what next ? Looked at the screw and bolt,decided to wrap some plumbers tape around the screw part.made a tight little hook on a length of the wire long enough to reach the hole where the screw meets the bolt put the screw in the hook and tightened the wire ( not to tight ) just enough to hold it and after a few minutes I managed to work the screw just enough to grab the tip of the screw and hold it gingerly ( just and no more ) the screw still connected to the wire so still holding the wire which was still connected to the screw managed to hold it all together and managed to get a little turn on the thread with the bolt ( phew ) one I had a turn on the bolt I managed to get it hand tight. This took about half an hour but it felt like hours.. It defiantly worked . The following day today I put the shelf back in ( phew ) again… Checked tightness appeared to be ok…Time will tell my Warranty is finished .. If need be will see if I can adapt Allan key to tighten from cavity… The told me they have never had such a thing to deal with it just doesn’t happen (yea right )