6 Gal Hot water tank

I take it your water heater doesn't have an electric element for heating....gas only and you want to 'convert' it to electric heat.

After market elements kits are available (Hott rod & Lightning Rod)

They screw into the drain hole (1/2" on Atwood Brand and 3/4" on Suburban Brand), have their own t-stat and plug into an outlet. You just have to provide the outlet.

Suburban Brand requires the use of an anode rod....the kits come with a small rod.

And BOTH MFG. do not recommend using a drain hole heating element and will void warranty if used.

Now IF your water heater came with electric heating element....those are std.

You must have an Atwood water heater. The only element that will work is a Hott Rod which is not recommended by Atwood to be used in their tanks.
Hott Rod