Dropped Fresh Water Tank

[mok]

We have a 2008 International 23 CCD that we bought new. It has approximately 15,000 tow miles, with the last tow last September. I filled the fresh water tank last week to sanitize, and began washing and waxing the trailer. Lo and behold, three of the four brackets holding the tank came loose and it came crashing down. We have examined the bolts, brackets, and bottom of trailer for rust. Found none. The trailer repair guy (not Airstream) said the holes were stripped - he could push the bolts into the holes by hand and watch them fall back out. Is this unusual?

He put the tank back up (after a tremendous effort to empty it) using 5/16 self tapping screws. He recommends either: adding four additional straps with 8 additional self tapping screws, or using a hole saw to make 8 holes to use a snake to fish reinforcing plates and 3/8" carriage bolts with flat lock nuts to put the original straps back, then plugging the holes. Anyone have thoughts?

[Alumaholic]

I would not use self-tapping screws for that application (though my 2007 was probably manufactured with them just like yours). By its very nature, water in a holding tank is almost constantly sloshing, oscillating, and otherwise working in conjunction with gravity against the self-tapping screws. For this reason, Airstream was once very careful to through-bolt the straps and brackets that supported any holding tank.
In the 70's the fresh water holding tank had a long, 1/2 inch (I think) bolt that passed up through the center of the tank in its own molded tunnel through a frame member above the tank. This supported the tank in addition to the additional support brackets.
Sound like your tech is a good one. The four additional straps should do the trick.