True, with PSI its not the P's that get you, it is the SI's
Sure just an ounce or two could get crazy amounts of "crush" going on on a big ship. It would have to be spherical, or at least mostly cylindrical to use circles to stand upto the compressive forces, and even then it wont take much to implode it.
But imagine as you get a few milibars of vacuum, and see the sides start to suck in, you hit the Heater Element to bump up the temp, thereby bumping up the pressure to "ease the squeeze". Over a period, and in balance, you suck 1/4 atm vaccum, and heat the gas to a 33% expansion... you have 75% the weight without the crush. Of course, I'm just throwing out a swag as to the temps involved to get a 33% expansion from 80degree nice day air- could be it would melt the envelope.
anybody have the interest to crunch the PVNrT numbers for temp change to get from N to 3/4N? or from 1atm to 1.33atm if that floats you boat.
oh, You dont happen to have the weight/density of Helium at 1atm?