More power to Mike Glynn for engaging with them. I often tell him he's thumping his head against a particularly hard brick wall. There is no test possible that would convince these people that it's simply condensation.
My personal favourite from peekay is that clouds don't happen at 35'000 feet. I've often wanted to take photos of cirrus out over the pacific but I'm sure they'd explain that away as chemtrail testing, residual chemtrails from previous flights, etc.