Proper mask

I can't help much with your question, as I'm having similar problems. I tend to stay away from hard-edge camo schemes for this reason.
But, welecome to the forum!!

IDFModeller hi and welcome...



try tamiya (or similar) modeller's masking tape; easy to use, comes in varying width rolls and won't rip the paint off underneath when you come to take it off.
hope this helps.
regards,
nick

If it's straight line your after (and you're not masking too much) you can use wetted paper to give you a straight line.

Don't make the paper too damp, just enough to stick to the model. Apply the paper, spray then remove. No messy adhesives left behind. Mind you, you may still need painters masking tape (blue in color) for more precise patterns but, the paper works pretty well.

I just finished a complicated paint scheme on my Sturmtiger. The original was a hand-painted, hard-edge scheme, but I wanted to airbrush it to avoid brush strokes. Since I had 5 view color art work, I scanned it in, scaled it and printed it onto Avery removable Sticker Project Paper. I then cut out the pattern and used them as masks, but they only worked on the vertical and horizontal surfaces. I filled in the rest with Micro Mask. It took Best of Show at my local Hobbytown and now it's reloading for the upcoming IPMS show, where I'm sure it will create havoc!

Thank you very much guys, it was very helpful, I'll try.