Looking for a lowboy water heater for a 4 ft crawl space. Currently have a 40 gallon one which is 21 years old! The problem is we want to continue using natural gas one and the only ones we can find are electric. Have been everywhere looking can't be over 35 inches tall and 25 inches in diameter. Are there 30 gallon ones that fit this description and if so is it possible to replace the one with two 30 gallon ones?