side frame rust through/rot

[FC_fan]

car: 1986 rx-7 N/A

well I have 2 trouble spots.

one is on the drivers side. the rear of my rocker is rusty and the last 6"-7" of the side frame is gone/ needs to be replaced (that includes as far as I need to cut back onto solid metal). looks the rocker has been bondo'd over by the previous owner. anyway, I was thinking of using a carbon fiber I-beam to put inside the side frame as it would be light weight and strong. what do you guys think? I will be spraying metal ready and POR-15 all over the area inside and out to try and prevent further rusting as well.

The second is on the passenger side on the corner right behind the front wheel well and under the front fender. the entire 6"x6" section is swiss cheese and distorted from jacking weak metal I think (my pinch welds under the car are all bent from jacks too on both sides of the car). I don't know how I should fix that section. it looks like a pretty complicated area. maybe build a small metal "box", coating the inside with POR-15 (just in case, don't want it rusting from the inside out). then put that small "box" in that corner and weld it up good to all the surfaces it touches. I'm not sure if that would be that best way to go about it.

I'm open to ideas are direct me to threads who have dealt with this problem. I have to fix it, these cars are rare around VT. My brother (89 FC) has a parts car in demo derby condition but these sections are almost as bad as mine so I think fabrication and creativity is the way I need to go. thanks guys.