We've had ext. warranties (EW) on some of our previous RV's but have elected not to get one for our current Axis. Biggest problem that, like many others, that we experienced with them is getting the 'prior approval' before any work is done. This can sometimes take days and even longer if the EW company you buy from doesn't staff their approval office over weekends. So, if your rig is immobile, you may be waiting for a while. Better to just call whomever you can get to respond and get back on the road. And, over time, its often less expensive than the thousands of dollars you'll pay for an EW. Also, remember that if your problem is with the chassis, the vehicle manufacturer's factory warranty is usually good for 3 years or 36k miles. Finally, if you have some common sense and you're the least big familiar with vehicular electronics and repair, and you can read repair instructions, such as those posted on this forum by Ed Felker, you can handle many repairs yourself.
This manual is mainly for Axis and Vegas units but many RV components are shared by various models, so you can get some good information, whether your's is an Axis or Vegas or not.