FreeBSD-12.0 Install: mountroot> ?

[Clay Daniels Jr.]

Trying to install FreeBSD. It boots to the USB image, and gets through the
first two pages that are shown in the Handbook. Then it tries to locate the
partition to install to, and give me the mountroot> prompt. If I enter "?"
it gives me a list of partitions from ada0p1 to ada0p9.

This is what the current partition looks like in my Fedora bash shell
terminal:
cgdisk 1.0.4
                                Disk Drive: sda
                           Size: 976773168, 465.8 GiB

Part. #     Size        Partition Type            Partition Name
----------------------------------------------------------------
            1007.0 KiB  free space
   1        1023.0 MiB  Windows RE                Ba
   2        360.0 MiB   EFI System                EFI System Partition
   3        128.0 MiB   Microsoft reserved        Mi
   4        192.0 GiB   Microsoft basic data      Ba
   5        128.0 GiB   FreeBSD UFS               Basic data partition
            156.0 MiB   free space
   6        1024.0 MiB  Linux filesystem          Fedora Linux
   7        127.0 GiB   Unknown                   Fedora Linux
   8        450.0 MiB   Windows RE
   9        15.7 GiB    Microsoft basic data      Ba
            5.0 MiB     free space
As you see, partition 5 is my target, so I enter:
mountroot> ufs:/dev/ada0p5
I get the message "failed with error 2 (unknown filetype system)"

Am I making a mistake to pre-format my FreeBSD partiton? I also tried
leaving it as blank space, but then there is no partition to target for the
install.

Also, I wonder if I don't have some GPT vs MBR problem:
[root at pavilion-23-attlocal-net dev]# gdisk sda
GPT fdisk (gdisk) version 1.0.4
Partition table scan:
  MBR: protective
  BSD: not present
  APM: not present
  GPT: present
Found valid GPT with protective MBR; using GPT.

Any clues would be appreciated.
Clay Daniels