Structural Foam for chassis stiffening

The original question was "have you ever thought about it."
The answer seems to be yes, many people have thought about it. In reality you have done more than thought about it and this thread seems to have convinced you to proceed.
More power (mo' par ?) to you for being creative in your approach. Far be it for me to criticize another's ideas and concepts. I just simply stated my experience of the product and its application.
By all means post your results and procedures including your list of materials and process. Please let us know the results after a few years to see if it's a viable, long term and cost effective option.
Good luck.