If you dip the canopy in 'Future', it should prevent the fogging from CA glues; it's the fumes that do the most damage. However, it's best to use 'Kristal Klear' or white glue, which will dry clear, and avoid the fogging problem.
The fit on the Revell/Monogram kit is due to the age of the moulds. When new, these kits were perfect.
The Academy kit of the P38 is really very, very good, far superior to the Revell/Monogram, which is to be expected, with current mould-tool production techniques. I built it recently, without problems of fit. Just a tiny amount of filler was required in the usual area - the tail boom joint, which aligned beautifully.