with my radio and kit ive found that I needed to do all three to get that bastard to stay put and feel solid.
with out the support (#2) on back of my radio it still wanted to tip down and slide out. it would then pop out even with the card board behind the tabs (#3) the only way i could put the support on was if i put the slot on top (#1). then i could attach the support im talking about to the radio. it will also let you adjust the tilt of your radio. your kit looks to be a tiny bit different so yours may very.
now that my radio rides that factory rail and i have the card board in, you cannot remove my radio from my dash with out taking the bezel off. its solid and cant be budged.
Toreador Red 05' FX4
4.0 4x4 A/Tran Ext.Cab Daily Driver. Nomads, BFG M/T's
Alpine 9857, JBL MS-8 DSP, US Acoustics 2x80w & 2x100w, Vifa 1" XT25 Dual Ring Radiator Tweeters 3k+ 24db slope, Dayton Audio 7" RS180-4 Mid-woofers 100Hz-3k 24db slope, 500w rms Kenwood Class-D Mono - JBL 10" GTO1014 Sealed. 100Hz- 12db slope