Hi Jodie
If you are looking for a permanent fixture then Sikalfex would be the way to go but just remember that if you are selling the van on in the future and wish to remove the panel then this may take some doing. What we advise is that you can get fixable mounts, the panel attaches to this mount via stainless steel T6 bolt then just add a little adhesive to the mount beats sikalfexing the whole panel!!
From experience and installs that we have done mounts are defiantly the way to go!
If your still unsure just ask