I got my new head unit and temporarily installed it to make sure everything works. My lower dash needs repair because the previous owner cut a hole too big for a single DIN unit. It is a nice rectangle but about 1/4" too big in all dimensions. the only way I see to repair this is from a panel mounted BEHIND the dash. I made one out of 1/8" hardboard and I will texture it and paint it. It looks like it will work but if it was you, how would you bond this to the plastic panel to make it strong enough to support the weight of the radio? I can only find one threaded hole near it on the backside for a clamp.

I would probably cut an aluminum or steel panel .060"-.125" (or around 1/16" to 1/8") thick that fits the front recessed radio rectangle tightly. Then drill a hole for a 10-32 button head screw in each corner. On the back side I would use a large washer on the screw to help distribute the clamping force over a wider area. Scuff sand the panel, prime and paint or cover with some fake carbon fiber looking stuff, I've even done panels like that covered with Naugahyde (vinyl) just use spray contact cement, apply and trim to the edges of the metal. It being recessed you wont see the edge.

I would probably cut an aluminum or steel panel .060"-.125" (or around 1/16" to 1/8") thick that fits the front recessed radio rectangle tightly. Then drill a hole for a 10-32 button head screw in each corner. On the back side I would use a large washer on the screw to help distribute the clamping force over a wider area. Scuff sand the panel, prime and paint or cover with some fake carbon fiber looking stuff, I've even done panels like that covered with Naugahyde (vinyl) just use spray contact cement, apply and trim to the edges of the metal. It being recessed you wont see the edge.

Okay, so I need to mount it to the front. Darn. I was actually trying to pull the radio faceplate inwards because it sticks out too far on this Pioneer. The faceplate is 1/2" thick versus 1/4" on my old JVC. Plus it is way too shiny, I prefer a mat-black.

Basically, what grzewnicki said. You can mount it from the back, but I'd double up on the thickness of the hardboard.

You'll need to support it from the rear, too. Even if the front were strong enough to suspend the head unit, the rear of it will bounce around like a diving board.

Yeah i plan to use some strap on the back to support it. It's looking like I need to remove the lower dash and replace it with a stock one and start over with cutting the hole.

I got some ABS plastic sheets and made a new hole. Glued it on the front side of the stereo hole on my old dash.. looked good.