Funnily enough I bought a similar type garage for my Morgan before new garage got built. The Z4M has to put up with living outside!
As a cautionary note, these can easily take off in high winds. I had anchored down according to the instructions, but awoke one morning to find the garage about 100ft away upside down over a hedge in next door field. Morgan escaped with only one 6 inch scratch which was quite amazingly lucky.
I recommend "dog anchors". They are huge metal corkscrews that tie in to the ground then use ratchet tie downs. I mounted them inside and pulled the metal roof bars down. All been fine since then. Bought half a dozen from ebay with ratchets for about £25.