Since he used what he owed for rent toward the taxes instead couldn't the owner just use that against him?
Do you have proof YOU paid the taxes?

Lets look at the bottom line here. You have been living basically rent free. Yes you bartered some for the rent (hope you kept full documentation of that). So, you either move or invest.

You moved into the trailer on a VERBAL agreement. That puts you at risk right there. If you want to live there, then make the repairs or pay someone to make them. Document whatever you pay out. Document your efforts to contact the owner to do repairs and collect rent. Pay your rent into an escrow account, until the landlord starts collecting. If repairs or needed, or taxes need to be paid, take it out of that escrow account and document everything.