As you have found out, it works best on the exterior. I have had mine for 9 years and I just ran it up the passenger A-pillar and to the exterior on the right front corner. I have had no problems. The Sungate probably does present interference but so do a lot of things when mounted on the interior. Good luck.
'95 9c1, pcmperformance.com 93 tune, Dynomax Ultraflo catback, K & N box filter, LT4 KM, 160 stat, 3.08 Posi.