After playing around with a few different ideas for the frame, I decided to start with a solid wheel base. For the steering mechanism I am using the largest hinges I could find at Lowes. I drilled one of the existing holes larger to accept the bolt from the bicycle wheels, then bolted it to the 2x6 that acts as the front of the frame.
For the back of the bike I am using the existing suspension of a mountain bike and attached it with a large section of all thread to the 2x3s that run the length of the frame. The suspension rod is attached using an old satellite dish mounting bracket. I still need to check how true the wheels are and if they hold air, but the wheel base is now complete.
A simple weight test showed that it could hold me and my daughter without any problems. Next I need to get the pedals attached and the chain and idlers installed. I also need to finish building the steering mechanism, and reconnect the rear brake and derailer. Once a seat is installed I should be able to drive it as a recumbent bike, after that I will probably work on the canopy, and lights, then install the electric assist after the fact.
I am really happy with my progress so far. Hopefully I will have it fully enclosed and electrified by the time fall hits.
Let me know your thoughts in the comments below.