There are no recurring or additional costs associated with protecting your Vault, compared to a non-protected Multiply Vault. As with any other Ethereum transaction, there is a gas cost associated with the vault being closed and the Stop-Loss being triggered. 

The stop-loss trigger is performed by Keepers, externally owned accounts (EOA) not associated with the Vault's owner. The gas costs incurred by these actors is reimbursed, and paid from the Vault's funds (either collateral or Dai).When you configure your Vault’s Stop-Loss protection, you can see a detail of all fees charged to the vault closing transaction.

Figure 1: Stop-Loss configuration box showing details on fees and costs

Once the protection is set up, you can see at any time the approximate amount of assets you will receive when the Stop-Loss protection is triggered. This value takes into account all fees and costs.

Figure 2: Estimated amount of assets to receive when the Stop-Loss protection is triggered