I prefer this type extractor Vermont American 21872 Straight Flute Screw Extractor Set, Red, 5-Piece - Tap And Die Sets - Amazon.com
instead of the screw type. Since you can't use heat without damaging the wall you will need to use some penetrating oil and a lot of patience. I like using PB Blaster, spray bolt with it tap the bolt several time tap bolt again, walk away for awhile. Do the above several times before trying to remove the bolt. If the bolt still won't move do the spray and tap again, eventually the lube will penetrate the the threads and break the rust bond. Another way would be to drill out the bolt with a drill without damaging the threads. Use a small metal cutting blade or a small file to cut a relief cut all the way through the threads. Once the relief cut it made use a small chisel collapse the bolt. You may need to make two relief cuts to get the bolt out.
Chuck & Teri, 1999 35 ft. Dolphin 5350, F53 Chassis with tag axle, Chassis build date 1/99 in Mexico, Banks System, Trans Command, Air Lift Air Bags on rear, Koni Shocks, Blue OX TruCenter, TigerTrak track bars front and rear, Roadmaster 1-3/4" rear auxiliary sway bar, 2013 VW Passat TDI SEL Premium, 1994 36 ft. Avion 5th Wheel. FMCA #F430129