First off, I'd like to say when we do restorations and sand the first round of primer NOTHING gets passed me unless it's something off to the side or a couple pinholes or divets but nothing major, and no dings, but I recall having trouble with hoods and just couldn't understand it. I learned that supports from the hood push up and down on the outer skin and are a real pain in the arse. Not only do you have to metalwork it with that in mind or use a mini air saw to un-attach the outer skin to the supports at times then re-attach it, but you also have to put in on stands with that in mind, in which you either use two 2x4's or two stands so only the outer edge of the supports are touching. Anything touching in the inside area of the supports WILL cause NIGHTMARES!
I have an example of this and it pisses me off to high hell!!! So we got a real trainwreck of a 67 Camaro. Boss didn't expect for me to get the messed up quarter to look perfect but I got this whole car show straight and know it cause how it blocked out. Everything was fine and dandy but the fricken painter took off the hood and put it on a stand like a moron. So when I go to block it( on stands the correct way) I can see clearly where the stand was cause there's now two high spots on the same area on each side. Those high spots were the foam adhesive pushing up on the outer skin. At that point it was too late to do anything cause I just blocked it and knew at that point the drama wasn't over cause now that I blocked it out and it's straight that metal the moron pushed up with the stands will at a later point relax back down which will create waves in my bodywork. So it got reprimed(prime#2), which it would have gotten anyways. So I then let it sit for days sitting properly on stands so the metal would relax while NO work was being done to it other than waiting for it to relax cause at that point any work done to it would just be a waste when the metal later relaxes and makes your work look like a surfing competition. So yesterday I guide coated it 5 times in a row and by guide coat and hand feel it felt perfect even with a 240 scratch so I reprimed today and when it was wet I saw it relaxed EVEN MORE on one area, but I know my work and I'm not fooled or am questioning my abilities anymore, this thing is moving and it's all because one person put it on the stand the wrong way.
So next time you do a hood and take it off the car, be very mindful of the traps that await. The hard part is that mos shops don't even have a clue about this. It's mind boggling so I spread the word whenever possible.
Also, be mindful of the supports when metal working. You must block your hood in epoxy before just throwing on mud cause you most likely have high spots as a result of this. An easy test is to hit the high lightly with a hammer. If it sounds hollow it's a normal highspot, if it sounds solid it's the supports. Depending on how bad it is and what the customer is paying I handle it in a couple of ways.
If the money is right and the supports are causing a bunch of highs and lows I separate the foam with an airsaw and metal work it and shrink it back down and even sometimes have to use a slide hammer to move the supports away from the skin. Then I use seam sealer to reattach the skin before mudding. This is something I often say, " I wish I just would have handled it that way even though the customer didn't pay for it."
If the money isn't right I find my highs and use a pecking hammer to make it a tad below even and sometimes you have to hit it hard just to get the support to move. I will always use my stud gun when necessary but the only difference is on the cheapie is I use a pecking hammer to peck it down, which is something I don't like to do but I don't like to be yelled at by the boss either, so there you go.
My two cents on hoods.