Unknown cracks on roof and bed

[RangerReviver1990]

Can anyone tell me what these are? Well, besides that it's a crack, obviously. I noticed one on the bed when I first bought it, but I noticed the crack on the cab roof a couple minutes ago. I looked it up and they called it "spider webbing", but nothing was exactly what I was looking for, almost looks like the multiple layers of paint have been compromised and it's starting to rust right there. The guy that had this truck before me coated this entire thing (literally everything) in black Rust-Oleum and I'm guessing he was either too lazy or spent all his money trying to turn this thing into a redneck mud truck to put any clear coat or whatever it's called. Has anyone else had these cracks on their trucks? Would a good place to start be to sand the area or get some of that lacquer thinner/paint thinner and see if it's just the Rust-Oleum layer that cracked? Because it still has the original factory paint work, and then some sort of forest green paint, and then the black Rust-Oleum, but it could've just gone through all 3 layers

 

[pentode]

I'll defer to all the bodywork guys but that looks like classic skim-of-bondo over rusty dents, dings or whatever and just the results of water ingress and continued rusting.

If that were happening on my vehicle, I'd sand/grind it down as far as I wanted to know about it (ideally all the way down, beyond the rust), refill with filler and repaint. Assuming it's not a show car/truck.

EDIT: those bluish streaks are rust seeping out of the cracks and staining the paint.

 

[Shran]

Something shrunk, guessing the primer. That in turn caused the paint to crack too. I don't think you have much to lose by trying to fix that yourself if you feel up to it, probably best to do it now and find out what's under there rather than waiting. If there is filler under it, the metal will rust under the filler (kind of doubt it by the looks of things though.)