Can the park charge the resident a late fee if they missed paying the rent and utility bill by one day?

Late fees on rents, utility charges or other pass-through fees are not regulated by the MRL, however, California court cases regarding late fees generally have upheld residential leases with preset late penalties if they bear a reasonable relationship to the actual damages that could be anticipated or sustained by the landlord for late payment, such as administrative costs relating to accounting for and collecting the late payments. For example, a 3% charge for late payments of rent ($15 on a $500 rent bill) is probably going to be construed as reasonable. Whether $50 is reasonable depends on the outstanding amount of the late rent and utilities owed.