Mike,
The newer design is much better. As Elliot alluded to, one reason for the "L" in L-girder is to be able to attach the decking from underneath so you don't have to figure out where the screws are beneath the landscaping if/when you need to make changes. You can still do that using small angle brackets they sell at Home Depot. Another reason for the "L" is to make the 1x4 more stable. Since you are using 2x4s, that isn't really needed for stability.
IMHO, there's nothing really wrong with using 2x4s, etc., that isn't what I meant by overkill. I meant the extensive framing and then more extensive crossmembers. I get why you want the crossmembers, to deal with the irregular shaped aisle. Your latest design deals with that much better and with a lot less work involved. I think you've got a workable solution, just consider attaching the decking from below rather than on top, unless you're sure you'll never need to make changes. 
You still have to deal with the access panel because you've added a rail there. good luck.
