can you start by measuring the temps outside the tent (over the course of a day) before trying to control those inside the tent? if your loft is too warm then you’re fighting a losing battle, because you have only got equipment that heats the air rather than cools actively.
if your loft is cool enough, then it should be a simple case of drawing more cool “loft” air into the tent when it gets too warm, that could be accomplished with an inkbird and a bathroom fan pushing air in through the bottom of the tent.
can you attach some pictures of your set up?