This is what I did.
Standard ali framed greenhouse, glazed with the hollow polycarbonate stuff. Didn't want a concrete base in case I wanted to rearrange the garden in the future.
So I found a spot and levelled the ground. I then plonked the greenhouse there.
"Drago,you maniac!", I hear you cry! "One good puff of wind and air traffic control will be able to track it as it heads for the north sea, you lunatic!"
Oh ye of little faith! I got 2 scaffold planks and cut them to the same internal length as the greenhouse. I placed them inside the greenhouse, one on each side lengthwise, but not up the to edge. I then used some dirty great stainless screws to attach the end of each plank to the bottom rim of the greenhouse. I then anchored it to the ground by the simple expedient of placing over a tonne of planters and tubs on the planks. Just to make it look tidy I sprinkled some bark chips mover the floor.
Sods law, in 5 or 6 years I've not felt the urge to rearrange the garden so I could have laid a proper base after all 🤦