I have one similar to this and is anchored into the ground like yours is. Its been up for about 3 years now and so far so good. However, we don't get the winds you guys get up north. Here is the 2 things I did to make me feel a little more at ease.
1. I stood 3/4 inch plywood up on the inside to make the bottom a little more heavier than the top and attached them with self tapping screws. Mine has metal walls all the way around on the exterior side so its enclosed. Screwing the plywood into the metal support legs on the inside were easy peezy with self-tapping screws and cordless impact drill. Hope that makes sense.
2. Placing sand bags on the bottom supports really put me at ease. Its cheap and very heavy. I put the sand bags down right after it was installed until I could get the plywood up and just decided to leave them there where I could. Very effective.
I'm thinking if you want walls, I'd use plywood first, then attach the metal panels over the plywood. I would fear the metal walls might make it more vulnerable to heavy winds. Dunno.
Since you have a 3 pt auger, you could also dig some holes and fill with concrete and use the footings to strap the whole thing down maybe? Kinda like they do with mobile homes? Maybe? You could even embed the anchors into the wet concrete. My dad has a porch that he strapped down like that. He ran the straps over the roof and anchored into ground. Instead of just anchoring the bottom, he has the whole darn thing anchored down. It is still working and it has been up for many many years.
Man, I'm good at spending other peoples money. And putting them to work!!! Ha.
