Supply Plenum not selaed?

[Paul DoCampo]

I have been replacing the entire duct system in my primary SFR (soon to be rental). One thing that has concerned me is that the supply plenum is wobbly and not very secured. I notice that it is tilting to one side and I can actually lift that side up to an extent. Its wrapped with insulation so I cannot see whats going on. But im thinking that it is not sealed correctly as well, and I may be loosing a lot of air once I turn it on. Any thoughts? Or is this normal and I have nothing to worry about?

Note: This is my first time replacing a duct system