I have the same van ('93) and I made a nifty front wheel chock + tie downs bracket which clips into the seat brackets. Currently, the bracket is for two bikes, but could easily have another wheel chock added for the 3rd bike in backwards.
I don't have any pics of the bracket at the moment, but I'll try to get a pic this weekend and scan for you when I get the pics back.
I also designed and built a two-bike rack for the receiver hitch with a hitch mount, so I could haul my four whler plus bring the small pop-up camper. Those E350's have some SPRINGS! :cool:
BTW, I have not yet added any floor liner (but need to), nor wall curtain (bike smell is a non-issue so far). I have left the roof air and floor heat in place; it gets hot AND cold up here.
Overall, the van seems to be a good idea, and I see more & more of the 15 passengers at the races. :)