f-150 frames

i have a 81 f-150 4x4 and the frame rales under it have holes from one end to the next made by the factory but they are 1"x2" and 2"x3" does this sound strange never seen a frame like this.thats why i am asking.and will it make it weaker for towing a 31 ft travel trailor thanks
jenn

Believe it or not.. that makes the frame stronger.

I remember one of my neighbors bought a 1980 F-150 4X4 regular cab brand new. He claimed it had a weak frame because of the holes in it and was afraid to haul a heavy load. If I remember correctly, the 1981 was supposed to have a stronger frame. If you don't get more answers here, I would do more research.

My 83 had the same holes and I used it for landscaping. An F100 hauling 1 tonne loads of soil and never a buckle. Don't sweat the holes, watch for rust around the shackles. Those can be weak points.