I've found that on planes that have flat surfaces with Monokote on them that the Monokote seems to lift and get air bubbles as the plane ages.  I have a Brodak 38 Special that is about a year old and the Monokote is getting loose on the large flat surfaces like the horizontal stab, elevator and the back half of the fuselage.  I find that I can iron it back down and poke pin holes to release the air bubbles and then I take a moist cloth and go over the hot surface to press it down.  I used the Metallic Red, Monokote brand.  I'm wondering if using Balsarite or something else will make the Monokote stick longer.  I think that I've read that elsewhere.  My edges have all stayed on tight, it just seems to be the center areas that lift.  Maybe I should be stretching the film on the flat surfaes when I apply it like when I do the wings.

Bout all I can tell you is the Monokote metalics suck. Even regular Monokote isn't what it once was. Most are switching to UltraCote, including me....

I'd have to agree with that.  I've found the UltraCote to be better.  The Metallic was hard to work with.  It's thicker and the wingtips especially, were a bear to get nice.  Overall the covering job got real nice but I struggled to get it that way.