Is it a stock UL1? Has the prop been changed? On smooth water, bouncing is usually an indication of the prop being too high and the boat running too loose. I can tell you that with my Vac-U-Pickle, if I have the prop height/angle wrong, I have bouncing issues. It can be CG too but I usually see CG issues in the turns, (it hooks). I see that the manual posted online gives some direction into how to change the strut height/angle as well as the rudder but doesn't seem to give the starting points that the stock boat should be set up to. Grim might know.
Unless you have made changes from stock, it should be able to run flat without adding weight, air dams etc. Those seem to be tweaks done after changing the motor/ESC.
I can tell you that on mine I start at about 1/2 inch from the bottom on the hull (at the back) to the center line for the strut and then add about 0.5 degree to keep the nose down. The boat should balance at the transition from the main hull to the sponsons and I haven't changed the rudder setup since Doug Smock built it.
Good luck. We have three UL1s at our pond and the guys have good luck with them and they run very well.