In case you still are interested in ideas for keeping the rudder down, here is my low-tech and simple idea I use for my Oasis. You only need a line and a smooth rvs ring (or something like that). I don't know if it fits your needs or will work on the revo, but it works for me.
I removed the lowest front bolt from the rudder and ran a line through it. I guess this is not a recommended thing to do, but I use this for about a year without any problems (I only sail at 20- mph winds in relatively calm waters). Of course it is possible and better to use a longer bolt and attach the line to that, instead of removing it.
I let the line run on both sides of the rudder mount (by which I mean the part of the hull the rudder is mounted to) and through an rvs ring. This way it comes at an angle that makes it possible to pull the rudder down ("lock") nicely.
If I think I need to "lock" the rudder, I pull it thight and make a slip-knot on the bungy of the rear deck. Because of the bungy, there still is some "give". It is quite a bit harder to have the rudder pop up, but on a strong impact it will, and nothing will be damaged. If needed, I can pull the line by hand to regain immedeate stearage.
As said, for me this setup works. I normally don't need to use this rudder "lock", but I made it because in late summer the weeds can be a problem on certain parts of the lake. They are (in fact the only) cause that my rudder sometimes pops up unwantedly.
Good luck with finding your solution,