Looks like you are well on your way! I fixed up a Spiderbox for my daughter that was in MUCH worse shape than yours was, I also worked with BDX and they were fairly good to deal with, I am not that impressed with their welding skills though.
Coating the top and bottom sides of the floor pans with thick bed-liner really makes a difference. I did that to ours. Used the Raptor kit from eBay, I also have it on my truck bed and it is decent stuff. I used 2.5 bottles which is a bunch but I put it on thick!
I got hubs and rims/tires from a Carter Talon, it really helped the buggy out and I like the aluminum wheels! I am going to graft the axle from the Carter on this thing next.
My daughter loves hers but they do need some sort of fender, she complains about all the dirt that gets into the seat so that is one of my next projects!
One last thing, reverse is sure a nice feature! You may want to think about adding it. I got ours from the same Carter Talon parts buggy I picked up.
