Platform for a sub enclosure in place of my rear seat

[DerrickC9035]

Hey guys so to start off I'm New to the installation process never been to a show before or even seen a big system in my life but I have always had a system in every car and a little over a year ago I decided I wanted to get into competitive audio and started building trying to put together a build I just got my power supply done about two months ago and I ordered a whole new system to go with it a 15" Incriminator audio TYRANT rated for 5K RMS to put the new AAK 6k on it with the AAK 180.4 for the mids and highs anyway I ordered a down 4 sound HD3 single 15 enclosure for the sub until I can get around to building a box for it and I don't know when that will be I still have to learn how to do it but the enclosure won't fit in the trunk so I need to build a platform for it to sit on in the rear seat area but I have no clue where to start because my gas tank is located beneath the rear seat area so drilling holes to anchor it or welding is out of the question any advice or help would be greatly appreciated as I said I'm new to this and really want to get this install done and move on to learning more things but I don't know how to get the platform to be lvl and hold strong enough for the enclosure to be put on it in the I can move both amps,fans , DSP, relay and everything else to the trunk with the SCIB bank