Bobber seat on a hardtail MTB frame

[RebelPrinter]

Hey Guys, Can anybody see a better way of doing this ? I am putting a bobber seat on an old Schwinn iZip. Front was easy, just cut down the seat-post and through-bolt with a stem bolt and a couple centering washers. Rear mounts are a little tricker. no welding.
I am thinking make a platform with that ply (3/4 birch, plenty strong). The front would be shaped to fit around the seat-post and fit the tube profiles. then bolt a piece of 1" angle iron across at the back to catch the seat springs. That vertical thing just in front of the tire is 1/8" aluminum plate and part of the old battery mount, and the ply would rest/be angle-bracketed to that as the rear support.

 

[DaLanMan]

My take on the wood... I would keyhole notch the front to mate up with the base of the seat (on the frame, not the post) it will natch have to be able to work round what is there.
On the back of that just put downlines (I would go with like 1/4" od Stainless if you can find thick wall even better, cot to size, find a shop to weld clamps or some kind of fixative point on to the bottom, do NOT thy this in a closed space evidently most stainless out gasses a LOT when it is heated (I am repeating this, even though it bothers me to let a potential deadly risk just go, better an extra warning causing caution than not risking that yog one moe black list ont that lovely clean slate

 

[RunForTheHills]

You could try to mount it to a strong rear rack, but the weight limit on most racks is usually no more than 50lbs. I think anything you can fabricate that is not welded steel is probably going to collapse from the seat bouncing around on it. They do sell sprung bicycle seats like the Brooks B67.