Tim: Really appreciate your help. I looked at all the Century Plastics battery boxes from your link with no luck. Century does have a nice box for dual 6 volt batteries but it won't fit my dual 12 volt batteries. But a good try and thank you for sending the link.
-My two Group 27 batteries are 25-1/4" long end to end.
-My 195BH modified battery tray is 8-1/2" W x 26" L. It will now accept my two batteries but not the two boxes.
-The two NOCO battery boxes (before cutting) are 30" long.
Gary has found the better solution, to cut and gorilla tape his two Group 24 boxes to fit the battery tray on his larger trailer.
Gary: First, you all must really be enjoying those hot pools at 1000 Springs with your trailer's maiden voyage. Wife and I are jealous. I use to go there as a boy when I lived in Twin Falls. Will have to stop there when our ID trips take us up that way. Have a wonderful time at 1000 Springs with your new trailer.
Your photos are fantastic.
I can see clearly how you cut the ends and tops of your Group 24 boxes. The photos and your detailed instructions will help me greatly.
I'll post some photos in April when the job is done.