What's the consensus on whether these are useful or should be replaced with another dampener? In my 23 XL Cargo van, they are in the back "windows" and in one bay of the ceiling. The other large areas I already put in Killmat. I'll have Thinsulate over all of it, which should help with sound as well.
Not very useful, but also not worth your time/money to replace them. It's not the sheet metal of the van body that you'll be hearing as you drive down the road. It's the silverware in the drawers, the tote of camping gear, the bikes, the slightly loose maxxair fan hood...etc. I can say this form years of experience living in my van.
Mass is mass when you're trying to dampen sheet metal vibration. Doesn't matter what it looks like. I left mine alone. Didn't know if the product I was using elsewhere would stick to the OEM stuff long term.