I know Nick I have never had a problem with the pleats on my pleats they always stay in place f I sit on them for long period of time yeah they wrinkle but they come right out.How deep are you pleats o your your kilt.
I know for a fact that when I pleatd up the Campbell acient tartan I did it to sett and it was approximatly 6"deep each pleat with a 1" reveal. But my Maple Leaf tartan the pleats are 3.5 deep.