Here is what I did:
- I "doubled" the spars under the car with rectangular tubes of 40x27 mm
- I made these reinforcements in the engine compartment:
- finally the bottom sleepers, inspired by what we find in the trade:
And as I have to replace the rocker pannels, I am installing a longitudinal folded sheet reinforcement that will be welded all the way inside and will be totally invisible. (I have not done any pictures yet)
I'm not a professional welder, it shows, but it's resistant anyway.