just a thought. I had kinda of a special requirement for the measurements of my aux tank.
I went thru Nationwide Wholesalers and they coordinated with RDS to have a tank made to my dimensions at RDS in Perry FL for less than I could have had it done direct. It was dropped at my door via the most economical shipper Nationwide could find. I am happier than a pig in you know what with it.
If Stephany still works there she gets it done thru her female counter part at RDS. The male salesman there is not worth the effort.
you can spec out where you want the taps, what kind of filler, where mounting tabs go, the guage mounting location, the works.