I want to splice 2 diffrent monokote colors together by over lapping them then taking the hot iron to them before i put on wing, now most wings have a sheeted leading edge and trailing edge with the center hollow now will this seam hold up when its laid over the hollow part of the wing and a heat gun taken too it or am i wasting my time?

I do this all the time, just use a piece of glass and put the lighter color down first (spray the glass first with window cleaner and then squegee out all water and bubbles). I use aprox. 3/16" of overlap and a trim iron set as high as you can get without causing the covering to shrink. You can also use MonoKote Trim Solvent. In either case I leave the parts on the glass overnite (not sure if that is needed using the iron but I do).

The resulting single piece of covering is then applied as you would if only using one color, almost any design can be made this way including camo pattern .

The transparent orange under the white on the "Bingo" in my avatar was done this way and is several years old. Practice on something small but it is much easier than it sounds.

Bingo -
The piece of glass w/ glass cleaner is exactly the way I do it. No problems at all taking it up as soon as its all tacked together. I've done four color overlapping schemes with no troubles. Kind of a PIA, but no troubles. And twister, believe it. It is easier than it sounds.