Can I backfeed through the second panel in my house providing that I make sure the main(first) panel has the main in the off position?

At first I said, HUH? Then I realized what you are asking.

The answer is a resounding NO!
You MUST use some form of transfer switch or interlock device. Period, and of story.
No matter how safe you think you or someone else might be, this can be a deadly setup.

The only reason is the interlock? Thanks

Of some form, yes. A transfer switch between the two panels would work as well.

I will not do it without a interlock! A friend is a electrician and said it could not be done! Even with the main(first panel) turned off.. thanks for all your help! WB

I am confused, but that is nothing new.

You have an electrician that is providing proper advice, and your asking here?