I'm interested to hear what folks have to say about the offset flanges. I've seen comments both pro and con. Does seen to often be a point of concern.
It may be worth considering not using the offset if there are any valid negative comments given the consequences if it fails. Leaking water (and I'm not talking clean water ) and structural damage not good.
Here's something you may want to check out if you could install a conventional flange with some moderate joist notching. You'll have to check with your local code authority to see if they would allow this.
I should mention that the newsletter sign-up and web contact us form seem to be broken on the site. You can call them at 540-334-4294 or toll free 866-METWOOD (also listed on the contact us page).