Originally Posted by OldCoot
Don't really think a few 5/16" dia holes in the bottom flange would be of any significance to the load carrying ability of the beam. Now if you notch the edge of the flange, that's a whole new can of worms.
Holes in the flange can cause a significant loss in section modulus of the channel structural section, the larger the hole the border the cross sectional area that is lost, ya-de-ya-de-ya ... I know how much loss can occur.
You are right that notching the edge of the flange is worse than a hole that is closer to the heel of the channel, especially if the bending is about the vertical axis of if there is buckling failure of the section.
The good thing is that the "box" portion of the RV adds to the strength of the whole, and reduces the load seen by the frame. How much is anyone's guess outside of the manufacturer's engineering department.
Bottom line - avoid drilling into the structural members of these trailers, especially when we don't know how much or where the margin is.