Tire Bead problems of the 2000 Chrysler Sebring

Both front tires have gone completely flat. Tire dealer stated that this is due to alloy rims contracting with the low profile tires. One was a newly replaced tire, the other tire had 11,00 miles on it. The right wheel is slightly bent, and I am told that this cannot be repaired and this could cause an incomplete seal around the bead/rim. I am currently checking tire pressure every two weeks, and most recently had pressure as low as 10 psi on rear right, and 15-25 on all others. Tire dealer stated this problem is due to combination of aluminum rims and low profile tires. This appears to be quite an unsafe combination if he is correct. I cannot believe that I need to reinflate my tires every three weeks! thanks for your assistance. (tiresize: p215/50r17).