Rustproof ? For my next car

Hello all, am about to trade in my Scion xb after 170,00 plus miles. Took it into the shop recently and looked underneath, noticing a " little rust" .mechanic said if I wanted to I could get the spray stuff at autozone...but that my car didn't have much rust.

now that I've decided it's time for it to be appreciated by someone who wants to give it a new home, my next car will likely have low ground clearance, and I live in the snow belt. So I asked one person in Sweden, and one in New Hampshire

Sweden said yes, undercoat
And New Hampshire ( of course) said no

So---join the fray,"