Need help getting crash dump

[vagabond]

Having trouble getting system dump after a (repeatable) crash.

10.3-RELEASE-p20 FreeBSD 10.3-RELEASE-p20 #0: Wed Jul 12 03:13:07
UTC 2017     root at amd64-builder.daemonology.net:/usr/obj/usr
/src/sys/GENERIC  amd64

I originally had crash dumps disabled, so changed
   dumpdev="NO" to "AUTO" in rc.conf
but still no dump in /var/crash after a crash and reboot.
   only thing in /var/crash is minfree, which says "2048"

On boot I see the message "No suitable dump device was found"
which I presume is the problem.

An issue may be my sys config, as /tmp and swap are memdisks.
Not sure how or if I can modify fstab or the config to get swap
on disk for a crash dump save since the disk has no swap or tmp
partitions.
 From fstab:
   /dev/ufs/hd250G1root  /     ufs     rw,noatime      1       1
   /dev/ufs/hd250G1var   /var  ufs     rw,noatime      2       2
   /dev/ufs/hd250G1usr   /usr  ufs     rw,noatime      7       3
   tmpfs                 /tmp  tmpfs   rw,mode=01777   0       0
   md99                  none  swap    sw,file=/usr/swap/swap,late     0  
      0

# gpart show ada1                                       notes
=>       34  488397101  ada1  GPT  (233G)
          34          6        - free -  (3.0K)
          40       1024     1  freebsd-boot  (512K)
        1064        984        - free -  (492K)
        2048    8388608     2  freebsd-ufs  (4.0G)       (/root)
     8390656   33554432     3  freebsd-ufs  (16G)        (/var)
    41945088  446452047     4  freebsd-ufs  (213G)       (/usr)

physical memory is 4G

Thoughts on how to proceed?