I have a Roadmaster tow bar that folds up on the front of the truck. It often stays there all summer. I wash the bugs off it now and then, and lubricate it with silicone spray as needed. No problems.
Oh, wait, last fall I did encounter a problem. The towbar had been in place so long that the adapters were rusted in place. I had a hard time removing them. So, I cleaned them and coated them with copper based anti-seize compound. If you normally leave your towbar attached, you might want to consider removing it for cleaning now and then. It doesn't take much rust to make it a permanent fixture!
When I was towing a Jeep, I had a fixed arm adjustable width A-frame towbar by Reese that stayed on the front of the Jeep. I used the safety chains to hold the bar upright. It worked great! Yes, here in Montana that is not against the law.