Any ideas how to fix this?

[Dirk35]

Short of that corner on the drivers side, you can replace all of that with little small peices of 20ga bent in the vise. It looks like a brake would make too sharp a bend. Its take about 4 different peices if you didnt hammer form it, but would be easily done.

[Beck]

Well if you are building a DRIVER and not a All out show peice,this is what i would do, and have done.   Grind area down to shiney metal,take duct tape and put on under side of holes, get some fiberglass, comes in kit, lay it out on top surface and aply resin. Or you could even use just resin without fiberglass clothe. After it sets up remove duct tape. Keep the vent,it will come in handy this summer.Just a little advice from a fellow Michigander ( bay City)       8-Bal

Sand blasting works better than grinding for this. It gives the glass something to "bite" to. Care has to be taken to not distort the metal with the blasting process.
Laying the glass up on the bottom of the panel creates less body work. Make the under side strong and use body filler on the top. The first coat of fiberglass reinforced filler would be the best. Then just finish it with regular filler.
Never use fiberglass resin without glass.
The best material to use, NOT duct tape, for filling a small spot you are going to fiberglass over is the reinforced packing tape (normall 3/4" wide with the strands of fiber running long ways). Use the tape to cover the hole with the sticky side away from the repair. Then double this up using more tape to hold it in place. The reinforced packing tape has the least contaminates that effect the fiberglass resin.
Fiberglass  resin is the bonding agent in body filler. When you get to the bottom of the can and it has gotten a bit thick it is best to get a new can. Some times that isn't an option, you know you just need a little dab, just add a little fiberglass resin to the filler on your board. It smoothes it out a bit. If to much resin is used the top of the hardened filler seems tacky. That is caused by impurities in the air that contaminate the resin. It won't be tacky under the top skin.
Beck

[40oz.]

this only took a few hours. cut weld grind hammer finish.