I have a 2001 Silverton 330 Sportbridge. My surveyor (Al Prisco here) told me that moisture meters are useless on these boats due to the material used. I'm not sure if it's the kevlar material or what it was. Since my boat does not have a cored hull, it makes sense. Instead, he used an infrared camera to verify there is no moisture and to get a pic of the structures, very cool. He also sounded out the hull the old fashioned way, with a hammer.
Mainship and Silverton were made by the same company, in the same factory (I believe) and are now owned by Egg Harbor. Give Lloyd a call at the parts area and see if he knows if you have a cored hull or not. Since you have inboards, the transom is not as critical as I/Os or outboards...but you don't want a wet one.
I'd fire the surveyor.