Insulating CPVC Plumbing Pipes and PEX Questions

Q1: What is the best product to use when insulating CPVC pipes under a mobile home?
Q2: If it is the rigid foam pipe sleeves sold at Home Depot, can the hot and cold pipes be insulated all the way to the surface of the electric hot water heater?
Q3: The trailer has skirting around it. Would the rigid foam by itself be enough to keep the pipes from freezing?
Q4: I'm fixing up the entire trailer to rent out again. Would you replumb with PEX?
Q5: If yes to Q4, I would want to use flairit compression fittings. Would this type fitting be OK?

Any insulation is OK.

If the temp. falls below 32º and stays here long enough, NO amount of insulation will keep the pipe from freezing. If the temp only gets that low for a couple of hours in the overnight, you might be OK. Ask around and find out what works for other folks in your area.

Flowing water is less likely to freeze, but insulation only slows the freezing down, it can't stop it if the area gets below freezing. Flowing water is constantly replacing the chilled water with (slightly) warmer water from below ground.