check out my build thread in project and research. after I cut my doors, we sheeted the inside and capped it with 18 guage . Doors are far more solid than stock, I can stand on the flat part with no problem at all. And anyone who's seen me can vouch, I'm no small guy
I didn't want to fill the inside, as I installed some speakers in the doors, and down the road I plan on fabbing up a pocket of sorts, a map pocket recessed into the door essentially. Also, one thing I don't like about the spray is it really takes away the ability to fix anything inside the door if it goes bad, depending on how you set up the door latches and stuff.
