I did this with my Kona. Right on the weld, its straight down to the aluminum on a weld. It'll be ok, as I have taken 4 foot to flat (on concrete) with it like that and it didn't explode, just my suspension bottomed out. You'll just have to live with the ugly scratches. Both my bikes have these nasty gouges around the BB and chainstays. Tape will only hold the moisture and grit underneath it. Your frame is aluminum so It wont rust. I'd just throw a quick dab of clear coat or clear nail polish on it, works just fine.