The bike I started with was a Cannondale moutain bike at about 40lbs stock. I placed the 360W kit and two UB 12v 18Ahr SLA's in panniers on the rear bike rack for another ~30lbs. The bike weighed in at roughly 75lbs fully dressed.
I found the bike was very clumbsy to ride. The weighting was very off with so much mass up top and to the rear. I built the bike primarily for my wife to ride after knee surgery and she found it uncomfortable.
The kicker was the hilly area we live in. The two batteries would get her to twon and back with no room to spare. Having my wife push the bikes was not what I wanted. I built a homemade trailer from scrap wood, conduit, and other bits. I mounted four 12v 18Ahr SLA's to the trailer enclosed in a cheap gym bag. The trailer alone weighs about 15lbs and the four SLA's are 52lbs (13lbs each).
The biggest improvement in in distance. I drove the bike for 21 miles before running the batteries out. I weigh 220lbs.
I have a friend who is a big bike addict and he said the original design with me on the bike was bound to break the stock spokes. Tandem bike spokes could be used, but only solved one issue, not the distance problem I needed to overcome. Plus the cost to re-rig the whell was more than I wanted.
The trailer in the woods might be an issue, but on the rough rural roads here, it works great and makes the ride much, much better.