Picture posting is enabled for all :)
The main thing with poly-houses is the weight, or lack of it. Some have bars that run sideways across the base, these can be weighted easily enough. I don't see the point in digging down. 1; it won't make it any more stable, 2; It means you will create a hollow for water to sit in, 3; your access height will reduce by that much as will your light into it.Not sinking it would also give you the option of moving it easier later if you wanted to.Just make sure it's held down firm. Square 2x2 posts at corners will give you anchor points and help against sideways movement. A few concrete slabs inside will give you a dry standing area to work on.Pic's...pic's...pic's.