I used Silent coat on the ceiling and wheel arches as i thought this is where it is most likely to receive most heat and wanted to get the wheel arches looking good with a reflective coating, for direct carpet application, but i used flash banding, very successfully on the side panel, followed by closed cell foam then foil blanket type stuff, remember its only to used to densen the panels to take out some of the tinniness. so it doesn't need to cover everything.
Ultimatley it's upto you, if you have a brand new spanker of a van then i would think twice about it but, if your taking on something thats a fair bit older, then perhaps think about investing the cash else.