I used to have a lot of trouble ironing Monokote into cockpits and other small places where a standard iron will not fit.

 

You can buy a tiny iron called a “trim sealing tool”.  I had one of these for a short time, but the temperature control was inaccurate, and the shape was not very helpful.  So I got rid of it.

A better solution to this problem is a butter knife.  Heat it on your iron for about 30 seconds and use it like an iron.  It could also be heated with a heat gun, but it takes a bit longer.  Heat is transferred a lot better by contact with the metal iron.

 

The knife will fit into tiny spaces where an iron won’t, and it will reach a lot farther than the trim irons that you find in the hobby store.  I used a butter knife to iron the entire cockpit of this Small Wonder built from RCM plans.

You can try the same trick with a spoon for ironing fillets and other concave surfaces.  Spoons have to be heated with a heat gun rather than an iron, usually.