Sheet metal specification for 740 floors

[jbg]

Dieselers,

This is more of a Volvo 740 question, not really diesel specific: what gauge sheet metal should I use to replace areas of a floor with rust damage? I plan to purchase some sheet metal to form, trim, and weld into the sections that I cut out. I have seen mention of 18-gauge on various car forums, but nothing Volvo-specific. Any input on this topic would be very helpful.

Thanks,