Agreed! I have a section of what my garmin thinks is a 20% grade on my commute, and that sucker is *steep*. Fortunately, it's only for 5 blocks... 5-7 miles of something like that must take you a good hour, more while towing kids.

How bulky are we talking? For light-but-bulky-things, I usually just strap them on to my back rack with bungy cords. It's amazing how much you can get to fit. I've also been keeping an eye out for a milk crate to stick on there, but I'm guessing that's too small for your needs.