Long PCR suggestion!

[KHUANG at CHEMVX.TAMU.EDU]

Hi, Netters,
After I screened EMBL3 library, I found my genes are in two phage DNA, so
I am trying to walking (this two phage DNA is overlaped). I tried TaqLong
PCR System (from Stratagene), but no succesed. The insert is about 12 kb, just 
high G+C (65-70%). People said it is not difficult to amplify <= 15 kb by 
long PCR. 
Does anyone out there have used sStratagene this stuff?
How about your experience for Long PCR?
Thank you!

Huang