I would not even consider supporting the rack with cotter pins. Your photo shows why. The sharp edges of the rack have distorted and nearly sheared the pins.
Like many things, it is a cost / benefit tradeoff.
If the pins hold, what do you get? A little convenience.
If the pins fail, what do you get? A lot of damage to your TM, much of it likely unrepairable. Plus whatever happens to the car behind you. Big stuff.
The question of how to handle the issue has come up in at least three threads on this Forum. Let me see if I can find them. In the meantime, Rick's solution is a really good one.
Bill
Start with these. They have a lot of good cross references within them.
https://www.trailmanorowners.com/for...ad.php?t=17639
https://www.trailmanorowners.com/for...ad.php?t=17611
https://www.trailmanorowners.com/for...ad.php?t=13525
https://www.trailmanorowners.com/for...ead.php?t=9785