Thanks for the tip. I'll keep trying.

What I'm trying to do is fairly simple. Also, having multiple layers of protection is nothing new in the realm of security.

The biggest selling point of Electrum (for me at least) has always been its ability to use an online watch-only wallet in combination with an offline signing wallet.  The only thing Trezor would add in my use case is the ability to store the offline wallet's mnemonics in a much more secure and convenient way than an encrypted private key on the offline computer's hard drive.    By comparison, using Trezor directly with an online computer is arguably less secure than the plain Electrum online watch /offline sign method. 

FYI, if somebody sells a hammer and includes instructions on how to use it to build a house, it does not mean the hammer can only be used for house-building.  Given the open source nature of the Bitcoin ecosystem, I believe that Trezor's creators fully intended people to come up with creative ways to use their product.

All that being said, I'm now looking into multisig to get the extra layer instead.