Having decay on boats and helis made sense when they spawned on the map (limit entity counts or whatever).
Now that they need to be purchased with scrap, they should no longer decay.
To be fully transparent, I play modded servers and my main base is always in the ocean.
Having to start every day by buying a new RHIB and miniheli is a bad player experience, wasting 30 minutes of time that could be used towards something more fun.
Also, as I play modded servers, to me, scrap and resources are abundant so for me the issue is simply having to go and re-buy, as it wastes time.
In a solo/vanilla situation, it would be frustrating because of the resources spent and time wasted, too.
If removing decay altogether from vehicles is out of the question , at least slow down the decay, allowing a fully fixed boat/heli to las 10/12 hours, making it possible for a player to repair his vehicle at the end of the play session,come back to it in the morning almost fully decayed, but it’s fine, it can be repaired again.
I didn’t measure how much time it takes to decay now, but as I work from home, I find little windows of time to check my base’s status, and the boats simply dissapear within a few hours