Del. Code tit. 6 § 4308
A contract may provide for the payment by the buyer of a delinquency charge on each installment in default for a period of not less than 10 days in an amount not in excess of 5 percent of such installment or $5, whichever is less, but a minimum charge of $1 may be made. Only one such delinquency charge may be collected on any such installment regardless of the period during which it remains in default. The contract may also provide for payment of any actual and reasonable costs of collection occasioned by removal of the goods from the State without written permission of the holder, or by the failure of the buyer to notify the holder of any change of residence, or by the failure of the buyer to communicate with the holder for a period of 45 days after any default in making payments due under the contract.
6 Del. C. § 4308