If it's a good one, better to have it and not need it, than to need it and not have it. On my car and truck I have Gieco, and they offer an aftermarket warranty if you buy a new vehicle, and is good for 125K miles. $250 deductible is the only down side, but if a $4K transmission goes boom, $250 is nothing.
I don't know if they offer one for RV though, but would be a good option if they do. Mine is used when I bought it, so didn't even come up.
Knock on wood, the only thing I had to repair on it was a bad main breaker, whoever installed it cranked down on the screw so much it stripped and eventually loosened up to the point if overheated and tripped. I have had to replace a couple damaged items, like the cover for the vent in the bath, and the flap on the range hood vent, one was from hail damage, the other because I forgot to lock it in place before travel. Overall, been very pleased with how well mine has held up since I got it in 2016. Only expenses were actual improvements instead of repairs.