I had ideas of doing something like the OP ask about on mine. Easy enough to build a trap shelf and the drowning part isn’t too big of a deal if you use a pivot rod through your float. I thought by using a drowner lock such as a piece of of sq tubing or a piece of tubing with about a 12” arm welded to it. The arm would reach out toward the trap and attach by a short chains. Once the trap is fired and drops so would the drowner lock. With only a short piece of chain connecting the trap to the drowner arm there would be no chance of the beaver not drowning.
This should work in water that only has minor level changes that remains wadable so the beaver can be retrieved and trap reset using the rod. Whereas I have water that fluctuates 2’- 4’ and it’s no fun to see you have a catch off the float and can’t get to it so the rod is out. I need to retrieve the entire unit without wading.
What would the 12" arm be for? Just use a regular slide lock.. Drop the chain off the front and then back under the float to the rod. At most the chain would be 3', probably less. You would need deep enough water of course. The places I'm talking about are a minimum of 5' of more. I'm just spitballing here. When the spring runoff hits the river rises 1-2' then its a mad dash to get the traps back. Floats would solve that problem and still be working for you. The only reason I'm considering this idea is because we definitely had some snapped 330's due to various reasons. Wave action, muskrats, beavers swimming w/ sticks in their mouth etc. They have their place though. With footholds, We had very few misses. If it was snapped there usually was a beaver at the end of the rod.