Well, I've pulled the trigger on installing a used 250W Bionx electric assist on Terrie's Tour II trike...  we'll see how she likes it!  The battery sits in a racktop Arkel bag.
 
I'm putting a 1.75" Marathon Plus on the back, both for cushion and flat protection.
 
There's a bit of a challenge as to where/how to mount the controller unit, but it'll get figured out.
 
Pics to follow, over the weekend.