You should only close it for cold weather, even then they can take a light frost. Cabbage and Cauliflower like mild temps, they shouldn't grow properly in a "hot house".

What about aphids and other bugs? You are right, it’s not a hot house kinda plant lol

To be honest, neither cabbage nor cauli need a cloche. To protect against bugs you can just use row cover which doesn’t get hot underneath. You could use the cloche for crops which need winter protection, not so much against cold as against damaging wind and rain. Lettuces, spinach and parsley for example.