Fortran & OpenMP: How to declare and allocate an allocatable THREADPRIVATE array - fortran

Question

I had a serial code where I would declare a bunch of variables in modules and then use those modules across the rest of my program and subroutines. Now I am trying to parallelize this code. There is a portion of the code that I want to run in parallel which seems to be working except for one array, gtmp. I want each thread to have it's own version of gtmp and I want that version to be private to its respective thread, so I've used the threadprivate directive. gtmp is only used inside the parallel region of the code or within subroutines that are only called from the parallel part of the code.
At first I allocated gtmp in a serial portion of the code before the parallel portion, but that was an issue because then only the master thread 'version' of gtmp got allocated and the other thread 'versions' of gtmp had a size of 1 rather than the expected allocated size of gtmp, (this was shown by the "test" print statement). I think this happened because the master thread is the only thread executing code in the serial portions. So, I moved the allocate line into the parallel region, which allowed all threads to have appropriately sized/allocated gtmp arrays, but since my parallel region is inside a loop I get an error when the program tries to allocate gtmp a second time in the second iteration of the r loop.
Note: elsewhere in the code all the other variables in mymod are given values.
Here is a simplified portion of the code that is having the issue:
module mymod
integer :: xBins, zBins, rBins, histCosThBins, histPhiBins, cfgRBins
real(kind=dp),allocatable :: gtmp(:,:,:)
end module mymod
subroutine compute_avg_force
use mymod
implicit none
integer :: r, i, j, ip
integer :: omp_get_thread_num, tid
! I used to allocate 'gtmp' here.
do r = 1, cfgRBins
!$omp PARALLEL DEFAULT( none ) &
!$omp PRIVATE( ip, i, j, tid ) &
!$omp SHARED( r, xBins, zBins, histCosThBins, histPhiBins )
allocate( gtmp(4,0:histCosThBins+1,0:histPhiBins+1) )
tid = omp_get_thread_num() !debug
print*, 'test', tid, histCosThBins, histPhiBins, size(gtmp)
!$omp DO SCHEDULE( guided )
do ip = 1, (xBins*zBins)
call subroutine_where_i_alter_gtmp(...)
...code to be executed in parallel using gtmp...
end do !ip
!$omp END DO
!$omp END PARALLEL
end do !r
end subroutine compute_avg_force
So, the issue is coming from the fact that I need all threads to be active, (ie. in a parallel region), to appropriately initialize all 'versions' of gtmp but my parallel region is inside a loop and I can't allocate gtmp more than once.
In short, what is the correct way to allocate gtmp in this code? I've thought that I could just make another omp parallel region before the loop and use that to allocate gtmp but that seems clunky so I'm wondering what the "right" way to do something like this is.
Thanks for the help!