you say that you have a bottle jack back there, remove your OEM jack and mounting bracket and build a custom box for the space. I had too because I have two amps, one is very large, and my box back there. I took my jack and pushed it almost under my seat from the back side (I ride with my seat pretty far back so it's pretty hard for someone to ride there anyway) and slid the bar completely under. I am looking into a locking bed cap to stash all my junk though. I'll post a picture later.
’03 S10 CC, thule roof rack, brush guard, painted to match bowtie, running boards, and vent visors, ’56 “chevrolet” badge on tailgate, air box mod w/ K&N filter, Gibson cat back exhaust, 100% synthetic Mobil 1 since day 1, Kenwood deck, tow package, freedom grill