you will next wind up with a 75 gallon tank if you can get it thru your
doorways like ours we run at 150F, oops you're in the attic.
recheck your 40 gallon gas hot water tank for replacement of the DIP
TUBE if you have rapid temperature drop on the output of your gas hot
water tank.
i would use a drain pan and drain pipe under each tank with a battery
water alarm [$10 home depot] in each pan.

see also for dip tube and other repairs:
http://www.waterheaterrescue.com/pag...hot-water.html