whats wrong with this? (trailing arm ?)

[68 short step]

when i was looking at the frame i noticed this on 1 of the trailing arms... it looks like there was something that connects both sides of the arm, but it is all cracked and weathered (corroded?) so is this "ok" to use like this? this truck will be used for hauling. both boats/jetski's and a$$... would trailing arm reinforcement plates be the best option to fix this?? last pic is the oposite side, this one looks good..