A water level. Which is a long long clear plastic flexible tube and you pour some water into. There is also the pitch of the water and drains that needs to be accounted for and depending on what your ground is and your weather you should look into the down straps being sure anchors go beyind the frost line as to prevent them from moving with the freeze thaw cycles. Also making sure it's secure. Make sure that you do skirting and insulation but leaving an accessable for repairs or maintance. That can keep it closed otherwise.