According to eBay, the dimensions of a tankless RV water heater are 11.1 X 10.2 X 4.8 inches. As of 2015, this water heater is available on eBay for $188.99 and weighs 7 pounds.
The dimensions of the ATWOOD G6A-7 6 gallon gas pilot RV camper motorhome water heater are 16 inches wide, 12 1/2 inches high and 16 7/8 inches deep. It has a capacity of 6 gallons and heats up in less than 30 minutes. As of 2015, it is listed on eBay for $225.50. The new ATWOOD RV water heater G6A-7 six gallon LP gas pilot light is listed on Amazon.com for $269, and its dimensions are 16 inches wide x 12.5 inches high x 16 7/8 inches deep.