Hooze, go with a set like these, made specifically for cats :)
I thought about them as they were just being marketed when I bought mine a few years back.
However they would have to have been cut for my drives
I hvae seen these on Magic Cats out of Havasu

http://www.danamarineproducts.com/Pr...TOKEN=30962851

thats a nice looking tab sys., but if you put them where the tunnel is, would you be able to use them to control air pack under the hull, as in getting more air pressure if you ran them down a little at higher speeds and use them to come up on plane?

I personally would not sponson mount trim tabs on a cat. Tabs are used for stability on V hulls. Cats do not need side to side stability. As far as behind the tunnels using them to pack more air...the air has already pretty much released from the hull and will have minimal effect on air pressure in the tunnel. However, they will have an effect at high speed as more of an aileron.

Hooze...I was thinking about your other post and your porpoising at 70mph? Cats will go thru inherent instability when they start packing air. Yours may be amplified by the standoff box and prop selection. I would try some different props. You could try a cleaver or try something with more cup than the prop you have. I run negative trim to plane then positive trim to start packing air (helps release hull) and when I hit 80 I trim down and watch my speedo climb and tach stay the same.