I agree with Flyboy.Don't waste your time trying to be inventive using spray can foam.More problems than it's worth and it's not going to do what you think it will do anyways.I had the "brainiac" idea a few years back when I was rebuilding my SeaDancer flying boat wing to try and strengthen the wings "D" tube area and give the wing more floatation in the event of a crash.The engine pod was mounted to the wing so in the event of a crash ,it was the wing that had to float well due to the added weight of the engine mounted to it.That was my thinking at the time.After building an entirely new wing(minus the L.E sheeting on one side of the wing) I set about using expanding foam to fill the forward "D" tube bays between each wing rib.I had used expanding foam before plenty of times so I was quite familiar with its expansion characters and the force behind it.Hence the lack of sheeting on one side of the L.E.After filling each bay with foam(kind of like making muffins in a muffin tin.......only less tasty[:'(]) I let it expand and set up.The idea was to cut off the over flow level with the top of each forward rib and then add the front sheeting and voila.NOTTTT!!!!!!I can't tell you how much of a mess this stuff is to work with.It just seems to get all over the place no matter how diligent and cautious you are.Cutting down the overflow was also an impossibility.I thought I could hot wire off the excess and give me a foam core type finish.Oh boy was I wrong.When that didn't work then I got out the long box knife blades and then proceeded to try and hack the rest off.Sanding this stuff?Forget it!Have you ever seen a grown man cry before?Oh yeah,before I forget to mention it,weight wise,you wouldn't believe how much extra weight this stuff can add.Yowzer!Well to make a long story short,this proved to be a utter waste of time and I ended up having to take Acetone to each bay and melt and wipe this crap out to try and salvage my new wing.What a !@!#%&*#% mess!!Good thing I'm as stubborn as a mule and have the patience of a cat or else I would have stomped the hell out of this thing that day I tell ya.After 1 litre of Acetone and an entire day of screwing with this dam foam and then having to remove it,I managed to salvage the wing and got it cleaned up again quite nicely.She was finished in the traditional fashion and went on to have a stellar flying career.R/C aircraft and expanding foam should never be used in the same sentence.........ever!!That's my soap box schpeel for t'day.Good flying guy's.