Actually, Monokote does just fine for trim work if you use the proper techniques. You just have to keep in mind that it isn't as porous as Ultracote so don't go trying to heat it up to apply it to another surface or it will trap the gasses that get released from the adhesive when it is heated. The best way to use it as trim over Monokote is to apply it using windex on the surface and applying the trim piece wet. You then simply press out all the air bubbles using a credit card, scrap of balsa or your fingers. Next wipe off all the excess windex and let it dry for 24 hours. Stays on just fine. You can heat up the edges a little to make sure they tack down well but most of the time it isn't necessary. If you have any Monokote trim solvent it can be run under the edges to really make sure the piece won't come off as well.

I haven't tried Monokote over Ultracote but with how much Ultracote shrinks you may run into problems if it is over an open bay without any support from behind because the Ultracote will adsorb more heat and shrink more than the Monokote which would most likely end up with wrinkles in the Monokote piece. There isn't any shrinking involved when sealing control surfaces (if you do it right) so either one should work fine for sealing your control surfaces.