I'd have to dust off my MetalSales spec book to make sure but pole-builders put garbage 29ga rolled rib over perlins all the time so I don't see why 5v wouldn't be fine over 1x4 batts @ 2'. 26ga 5v is a sturdier product than the above (about the only thing it's better than) so, in my opinion, I don't see a problem.
If you are worried about MetalSales warranty this product...
Sorry, not a big fan of MS.
Personally, I would not put anything that was not mechanically seamed over any open span. Any snap lock or lap joint panel actually should be put over solid decking mainly because any weight on the spanned area will stress and weaken either one of these joints. But, like I said, I see pole builders doing it every day.