Um, ALL my boats, past and present, were on a fully supported flat surface.
The one I have now has two tanks, 165 gallons each, at 6.5 pound per gallon, or 1075 pounds. Last boat had two 210 gallon tanks, 1365 pounds per tank. I want those tanks fully supported and anchored down. Tight.
Your surveyor must be a looney tune.
Are you certain that's what the report says? Or does it spoeak to the actual venting of the inside of the tank? Maybe there's a problem there?