Per this web page, they turn out all right if the builder has time:
http://www.largescaleplanes.com/articles/article.php?aid=209
…or you could buy a 1/24 scale F4 Phantom II to take it’s place
…just kidding.
I must admit, I have had my hands full just building the injection molded kits in my stash; never attempted to build a vac form kit [:$]
I have been tempted to try using the spray on insulating foam as a backing on a vac form structure from product packaging just to see how well it would work.
Much trimming would be required, of course.[^o)]
I’ve heard of that trick. Remember a story where somebody tried it with a foam that expanded to four times original volume.
I have noticed that when using the foam around the abode…[;)]
…ergo the “much trimming” required …[:O] [whstl]
Re: 1:24 vac Phantom; You’re… not… helping! 
I’ve got the FSM series on vacform kits in my library so if I do decide to build it, I won’t be working totally in the dark. Just the thought of all the scratch building required is overwhelming.
And you KNOW as soon as I get it halfway done, Trumpeter will announce an injection molded kit! [:@]
I know from experience that somebody always does that…[bnghead]