The deck frames are aluminium ladders with the ply bolted to it, this is what the 700 drilled and tapped holes are for. It gives me a multitude of attachment points. Because it's thin the ply has no option but to obey and be flat!
MDF... weight and dust plus trying to use conductive tape in place of rails could be extremely problematic. One small wrinkle and you get a derailment in a difficult to get to place plus MDF doesn't, in my experience, ever have a nice edge post-cutting. Cutting the grooves is doable, I just need a router. I have suitable guide rails for my saw and the right adaptor for a router. Getting the grooves accurate means it would have to be done on the mill though. I wouldn't want to do that, it would make an awful mess.