Maybe you've seen this, maybe you haven't...

[MrBuick]

So, I decided to do a little practicing with some modeling putty. I had a spare hood from a '68 Corvette sitting around that had a very recessed part because a hole was supposed to be cut in the hood for a blower. I decided to fill it, because I've done plenty of body work with putty but never really any large areas, and I've got another build that I actually need to do something similar on...anyway, I figured I'd get a little practice in first and I'm glad I did. I guess what happened is I used too much putty at once, and when it started to harden, it sucked the thin plastic area from the hood that was meant to be trimmed away into it instead of just filling the gap...it makes complete sense, I just never really thought about this happening. The more you know.........

[bobthehobbyguy]

When I fill in the the area on a hood with a cutout option I fill it with super glue and then hit it with accelerator. Then if there are small spots to fix I use putty. The other option is two use a two putty which cures by a chemical reaction and not the evaporation of a solvent in a single part putty.

[Exotics_Builder]

I will usually start first by trying to fit in Evergreen plastic to reduce the amount of putty. Follow with what Bob mentioned and use Putty (usually Tamiya) to fill in small spots

[JTalmage]

The white putty is bad for that. I hear the gray putty is not.

[Mark]

That hood doesn't have the normal "cut line" engraved on the underside; instead, the whole cutout area is recessed, much thinner than the rest of the hood.  Even just painting it can cause that area to sink in if you aren't careful.  The way to fill the recess would be with a piece of plastic that would build the thickness up to that of the surrounding area (or maybe a little bit thicker).  Attach that with either super glue or epoxy, grind it to the thickness of the surrounding area if necessary, then putty any gaps that appear.  Make sure the "top" of the filler piece fits the underside of the recess area without leaving a gap. 

For hoods with the usual recessed cut line, if you aren't cutting out the hole it's a good idea to fill the line to help eliminate "ghosting" on the top side when you prime/paint.  Thin lines can be filled with putty, thicker ones with thin strip styrene.  Whatever cement you use, try to jam the strip into the cut line.  After everything sets up, you can file/trim/sand to match the surrounding areas.