I really struggle when I read the word "investment" in any message discussing insurance (including extended warranties). Insurance in not an investment - it is something you buy to protect you from potentially large expenses you could not afford to pay out of your pocket. Liability for medical or property damages is certainly one of those, but accidental loss to your own property (house, car, RV) is a good candidate too.
But insurance for RV repair costs is a much more "iffy" proposition, and the restrictions in the typical 'extended warranty' policy make it even more so. It rarely make economic sense to pay for insurance on losses that are typically measured in a few hundreds of dollars, even if the likelihood of a claim is high. But as the cost and sophistication of the RV's systems goes up, it may reach a point where the risk of an expensive repair gets substantial enough to justify buying insurance for it. For example, diesel engines and generators are both vulnerable to high dollar repair costs. Over 5 years or so, a $1000+ repair is fairly likely and a several thousand dollar repair possible. But even at that, the insurance cost is high for the dollar amount at risk.