looks good...but I have a few observations...if you care for them...
1 you used 1-1/2" x 1/8" alum. flat stock for your 4 uprights, these ride fairly high with no load...with not too much weight these are going to flex from side to side as you lean the bike putting a heap of stress on a single alum rivet (1/8" by the looks of them) fatigue will have its way and then your load will shift in a violent fashion...
as was mentioned by pipedr bolts with lock washers would be better...
2. provide even the slightest bit of diagonal bracing from your 'legs' to the opposite side of the rack (side to side not front to rear) this will greatly reduce your gears want to lean more than you...(it will also increase the amount of weight you can put on top...
3. As has stated already cover those ends (even the rubber caps wont be enought to protect your backside if get rearended (which I sure will not happen...but better safe...)) the closeing off and back rest were a great idea...
I think you've got a great idea there and I like the "utilitatian" approach I often have my bike set up for solo and if I want any more baggage space I have to dig out the rack and screw around with it...I like the simple straight forward approach...nice job
