Do I need to obtain a reentry permit before leaving Thailand if I am applying for a visa extension?

My annual extension for yearly retirement is due on August 20 (Hua Hin). I will go in July to do the extension (30/45 days before) also with a multiple reentry permit.

At the moment of doing that extension in July, I do not have a reentry permit. I will leave the kingdom at 5 August until 31 of August. Means, I come back when the new extension is in power (including the multiple reentry permit). But leaving with my first extension with no reentry permit.

Do I have to get an extra reentry permit before leavin beginning of August? (I guess I have to do it.)

Sorry for the long explination, but I hope like that it will be better understood.

Thanks for your great help in this group.