Is there a trick to installing this cover?
Yes there is a trick. That's why I wrote up how I did it and got a good fit. The trick is to start at the front strap and loosen it until the seat can sit in final position and the strap is doing a good job of holding the seat cover from shifting. I then adjusted the next 2 back in the same way and got a tight fit on the cover with no cutting of any straps. Like I said before- "cussed'em fit" Nothing is made for our bikes anyway so get used to creative installations.
I have several of the Stearns seat covers. The plastic buckles on the straps are not all sewed on the same. Only two will actually let the buckles fit up under the seat. The rest put the buckles right where the strap needs to wrap up under the seat pan, or right on the frame, and it would be very difficult to mount the seat on the bike like than. YMMV
That's one of the problems I'm experiencing. Some of the buckles are just on the lower outside of the seat hitting part of the body work (plastic panels).
When you say "velcro cords", are you talking about hook and loop closures like cord wraps? What section in Walmart did you find them?