To underlay or not to underlay metal skins.

[les45-JAY]

I'm finally to the point of being ready to skin my pop-up to retro project (http://tnttt.com/viewtopic.php?f=50&t=70991). Picked a metal vendor and ordered the skins this week and hope to have them delivered in about two weeks. My plan had been to use the 5mm Revolutionply as an underlayment for all my wall skins but as I look through the canned ham restoration Youtube videos it looks like most people just staple their skins directly to the insulated wood framing without underlayment. I figure the underlayment will add about 80 lbs to the build so I'm not worried about the weight. I already have the plywood that I salvaged from a previous project. Any thoughts on the pros and cons of this issue?