Hi
Best thing you can do is cut the rust out and generously remove even out to the good metal. Then make a pattern from card board or paper of the general shape of your patches....
Weld on the patches in small welds ( like 1 to 2 inch increments) so's not to warp, or over heat one spot. Weld one side then the opposite side in small increments to prevent warping. Smear the weld seams with Seam Sealer to finish it up.
Check out my build I replaced the whole floors both sides and the whole trunk pan. It came out real nice.
Good Luck
If you have more time than money,try to repair the floor pan. Year One offers a complete floor pan,if money is no object with your cars.Not that hard to in stall,read up on it,then take your time.Hope she turn out good.Mine did!