It sounds like your problem is more with your spraying technique than anything else and it is almost impossible to teach that over the internet. I am very much a novice at finishing but have switched to KTM-9 (after first using nitro, then StewMac water based) and it will be my finish on everything in the future. I used Z-poxy to pore fill, then shot the KTM-9 directly over it.
I use a small detail gun (what an auto finisher would call a "jamb" gun) with a cheap little home compressor. Water filter in the line and pressure set about 45 psi, practice spraying medium coats that look wet when they go on, but not so much that it runs. I clean my gun with denatured alcohol which I leave in the cup - for the next coat first mist a little alcohol on, dump the cup out and fill with the KTM and shoot - the mist coat makes the previous coat slightly tacky and the is supposed to make them melt together. If you get a run or a little orange peel just scrape and sand to about 320, then shoot the next coats.
Get enought coats on (15 to 20 or more) before you do the final color sanding and buffing. As you know, you can also brush KTM-9 - you just might have to do a little more leveling. There pretty good instructions for KTM-9 at LMI and here is a picture of the first one that I used it on - don't give up on it so easily.
