I'd use the blank cover with the knockout and a 90 degree FMC connector (shown below) and run the FMC stapling it to the edge around the storage bench. Then terminate it in a metal old work box. Connect the ground from you FMC to the ground in the old outlet box, either a grounded metal box or NM cable ground. At you new outlet box, connect your ground wire to the metal box with 10-32 grounding screw.

Check your breaker size to determine the wire size you can run: 20 amp breaker- #12AWG, 15 amp breaker - #14AWG.

You might luck out and be able to get a short piece 8' of FMC commonly known as a whip that comes with the wire and maybe connectors.

I'd use the blank cover with the knockout and a 90 degree MC connector (shown below) and run the MC stapling it to the edge around the storage bench. Then terminate it in a metal old work box. Connect the ground from you MC to the ground in the old outlet box, either a grounded metal box or NM cable ground. At you new outlet box, connect your ground wire to the metal box with 10-32 grounding screw.

Check your breaker size to determine the wire size you can run: 20 amp breaker- #12AWG, 15 amp breaker - #14AWG.

You might luck out and be able to get a short piece 8' of MC commonly known as a whip that comes with the wire and maybe connectors.

I'd use the blank cover with the knockout and a 90 degree FMC connector (shown below) and run the FMC stapling it to the edge around the storage bench. Then terminate it in a metal old work box. Connect the ground from you FMC to the ground in the old outlet box, either a grounded metal box or NM cable ground. At you new outlet box, connect your ground wire to the metal box with 10-32 grounding screw.

Check your breaker size to determine the wire size you can run: 20 amp breaker- #12AWG, 5 amp breaker - #14AWG.

You might luck out and be able to get a short piece 8' of FMC commonly known as a whip that comes with the wire and maybe connectors.

I'd use the blank cover with the knockout and a 90 degree FMC connector (shown below) and run the FMC stapling it to the edge around the storage bench. Then terminate it in a metal old work box. Connect the ground from you FMC to the ground in the old outlet box, either a grounded metal box or NM cable ground. At you new outlet box, connect your ground wire to the metal box with 10-32 grounding screw.

Check your breaker size to determine the wire size you can run: 20 amp breaker- #12AWG, 15 amp breaker - #14AWG.

You might luck out and be able to get a short piece 8' of FMC commonly known as a whip that comes with the wire and maybe connectors.