I have always used Ultracote and had very good luck. However, I need something to to seal my gaps and wanted to use Monokote. The reason is, I have a credit at Tower I want to use. Is there a big difference in application between the two? I mean, I am not covering a plane here, I am sealing the gaps. I have used clear ultracote on my last few planes, but have run out...

ultrakote is low temp, monokote is high...

for hinge sealing either will work fine, but for trim use you should only use ultrakote on top of monokote, not the other way around...

the ama actually has some good advice and coverings
http://www.modelaircraft.org/0704_1.asp

Be sure you use a covering iron that has good temperature control. I use a coverite thermometer for accuracy. Check the wrapping on each product and you will find a recommended temperature for application. Believe me there is a difference. I built an airplane for another pilot on the ocndition that he would supply all the materials. It was a two color covering job and he gave me some Coverite and some Monokote. Slowed down the covering job while the iron changed temperatures. Smokingcrater is right about the sequence.
Coverite on Monokote but not the other way.

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.

I agree with FlyerBry, that's exactly how I do it and the results are fantastic.

Second the motion by FlyerBry. Monokote trim over coverite or other monokote works with Windex. Other window cleaners that do not have ammonia won't work.

I'm curious as to why ammonia? I've done lots of automotive window tinting, and there we AVOID anything ammonia like the plague, unless you are removing tint. ammonia does a great job of eating away at adhesive. (want to remove a dealer decal from your car? spray windex on, then cover it with saran wrap and tape it down, it will fall off in the morning)

anyway, anyone try a couple drops of dishsoap with water? that is a favorite for tinting.

Dishsoap works great for decals that have a sticky adheasive because it lets the decal (Or window tint) slide into position before it sticks, but a heat activated adheasive needs something to activate it - like heat. Ammonia will also activate it, and once the ammonia evaporates (Which it can do since you're not covering it with plastic wrap) the covering is stuck.

Well I think that is the point - ammonia activates the adhesive by essentially dissolving it - then since ammonia is volatile it evaporates, allowing the solvent to dry/stick.

BTW, I used the windex method when putting some white checks on the wings of my red 4*60. Worked ok, but I found that I had to iron everything down the next day. So does the windex not work as well on oracover/ultracote?

I will also note that the 4* came with stick-on decals with very aggressive adhesive - the kind that usually stick where you don't want them to. Luckily, the instructions said to use Windex, which made placing the decals a cinch. It would have been nearly impossible to get those giant, long, skinny emblems on straight and bubble-free w/o the windex.

On some of the insignia from Major Decals they warn about using any window cleaner with ammonia. I'm sure soapy water would not disturb the adhesive and allow repositioning. When Major Decals are on they stick forever.

monokote will work similar to other films but smokecrater has it backwards -ultracote takes more heat and creates less gasses during application than monokote. hence, it is much easier to apply. it is also thicker than monokote and does not always go over open areas especially small ones like open stabs with out some wrinkling / loosening. also agree mixing the two for trim not good idea generally. also found ultra cote fades differently than monokote.