I have a 2004 Itasca Horizon so I think I can point you in the right direction.
Your KES is no longer made, and for years everyone said there was no easy fix to replace the SCS-Frigette system.
So for 3 years this was always on my to-do list. Well, last summer I found a solution the average handyman can follow to remove the guts of the the "Custom Engineered Security System" (aka KES) and you can replace it with a $25 Universal Avital 3100LS system you can buy on Amazon... which also comes with 2 remotes.
We also recommend you add a siren to scare skunks way and other undesirables... when you hear something or smell something outside and want to scare it away.
Here's the website link:
SCS-Frigette Keyless Entry System (KES/RKE) Replacement TO Universal Avital 3100LS
http://www.irv2.com/forums/f101/scs-...ls-451241.html
Don't worry about the rats nest of wires. Once you open the door and lift all the other wires out of the way, you can unclip the OEM wire harness and wire everything up on your bench... using the wire diagram in the link above.