There are other factors that need to be considered even with the tank being placed on two load bearing walls. Is your foundation bricks, blocks, or poured concrete? Above that corner of the house is there another story or stories? Is there a bathroom on that corner of the house where someone will utilize a bath tub? Believe it or not all of these things add stress to those load bearing walls and every wall has a max threshold. If your not sure and wan't to save yourself a huge headache just contact a local contractor and set a time for them to come look. They will normally do this for free or charge a fee up to $100 depending on who you contact. In the end at least it will give you peace of mind knowing you have taken all the right steps to doing it correctly.