By far tankless is definitely the way to go. I recommend checking out the Furrion RV Tankless Water Heater - Gas - Automatic Pilot # FR68SR. The great thing about tankless water heaters is the on-demand hot water, eliminating the need to wait for the water to heat back up.
This unit measures 12-5/8" wide x 12-5/8" tall x 19-1/4" deep and has cutout dimensions range of:
Width: 12-3/4" to 12-13/16"
Height: 12-5/8" to 12-3/4"
Depth: Minimum of 23-1/2".
As long as your current water heater... view full answer...