Any tips for taking sag/dents out of my roof?

From what I can see it looks like your framing (side to side) has sagged. Which means taking the skin off the roof. I've owned three campers and has the same problem on each one. Over time the snow especially causes the thin 3/4" pine to sag. But time itself causes all things to sag.

On our Compact I added extra framing to keep it straight. I've heard of some people using oak or other hard wood instead of pine. Although nothing will stop it from sagging if two feet of snow sit on it this winter.

I wonder if increasing the bows will change how the roof skin fits? You might be swapping one problem for another.

I am worried that might be the case.  One of the main reasons I started this thread.

A 2X4 the height of your trailer's inside, including a 2'cross piece of 2X(looks like a T when assembled) with a piece of scrap carpet affixed to the cross piece so it doesn't scratch the ceiling. I use a 12" square of plywood on the floor beneath the T bar so I don't dent the flooring. Measure your wall height floor to ceiling where the sag seems to be (measure at the wall, not at the sag)and that's the height you want the bar, which will include the cross piece, plus padding, plus floor protection. I install mine by first setting the top bar where I want it on the ceiling and then pushing the bottom of the bar along the ply on the floor (don't want to scratch the shellac) until it's in place. I use mine for support when I'm working on the roof.
Did that make sense?

You might try using foam insulation if what you have now is spun glass stuff. The big boxes sell it in 4X8 sheets, several thicknesses, easy to cut, and some here say it insulates better too. It won't crush easily.