We did the same job with our 1966
22' Safari, and we didn't insulate the PEX or isolate it any more than the original tubing. If I remember correctly, the water lines we took out of that area were rubber tubing--probably less heat-resistant than the PEX. Also, there is some distance between the back of the stove and the area where the water lines run.
We'll see how this works. Have only used the stove a couple of times since the water system rebuild, and the oven only for some quick batches of toast.
Glad to find another '66 Safari owner on the forums!