@chloroformus

Common practice is to apply for one tracker in the same giveaway thread.
That way more users have more chances to win an invite.
There is no official rule AFAIK, so if you desperately need more that one trackers in the same giveaway thread, it is not prohibited to state it in your post.
But it is not encouraging also.

Besides, applying to a giveaway thread means that you have ...officially applied, and you are considered a candidate for the invite.
Then, it's up to the user who kindly offers the invite, to communicate with you or not, or to wait for more applicants.
No need to apply or post for a second time.

Regards.