Tick what needs work. See a Bay Area cost range, which jobs need an HCD permit, and the repair programs you may qualify for.
HCD or your city, before work starts
In most parks it's HCD (state). A city or county can take over park enforcement with HCD's approval. Look up your park in the HCD park search to see its enforcement agency, or call HCD Codes & Standards, 800-952-8356. Work on the home itself (water heater, furnace, re-roof, panel, plumbing) gets a permit before work starts, even like-for-like.
Ken will reply with which program to call first and what papers to have ready. No spam.
408-666-2825 Many people get this wrong: "a water heater swap doesn't need a permit." In a mobile home it does, even like-for-like. HCD wants the permit, the manufacturer's specs and, for gas, the piping calcs. California also requires the tank to be strapped for earthquakes. Skip it and the buyer's inspector will flag it when you sell.