Ha Ha, looked all over the boat and can't find any humpy bits, what's a humpy bit?
I'm guessing were talking about the rear sponson, I've similar concerns and the two main issues to me are the forward angle may end up acting like an airfoil forcing the rear up and nosing over or as you state just the mere size of it could impact water turbulence with the same nose over effect. The issue is that the tub sits 1 1/2" off the water so in order to run horizontal the depth had to be matched in the rear sponson. In viewing all the riggers I've seen online to me most are designed for racing circuits and set up to do just that, my focus is on creating a rigger that is deeper wider and able to run at low or high speeds, launch on it's own and run on mild river conditions so I won't be restricted to waiting for ideal water conditions so in all a more user friendly boat, hopefully. Uncharted territory my friend! Another point I'd like to share is in the overall design I have in the back of my mind that if I wanted to downsize it is a simple matter of building a smaller motor mount and changing the rear sponson's to the side to shorten the boat and plunk a 46 engine or similar so that is in part why I've been what may seem preoccupied with the overall weight.
In another thread I considered using an aluminum foil rather than a sponson but haven't been able to come up with a viable design so it evolved into the rear sponson you see. The only other option I can conceive is to make two sponson's and lengthen them from the rear bolt on the tub to about the length it is now and each of those would be about 1" - 1 1/2" wide and about 9" in length. You mention the sharp cut of the sponson requiring a possible bigger rudder to compensate, that is why I earlier mentioned angling the trailing edge sides of the sponson to about 30 degrees or so in order to obtain a little give in the turning, I still will likely do that regardless of what route I go in the final design. The sponson spacing will likely be about 24" when done, I only set it up quickly on the table for the pic.
For finishing, well paint seems to be what I'll be doing with some hand painted design here and there. I have given this some thought so here goes, the name of the boat will be Slew Shark and the meaning of that is "
turn or slide violently or uncontrollably in a particular direction" according to the dictionary anyway, I hope it's the violent slide rather than the uncontrollable part. The paint scheme will be sharks teeth around the front of the tub and the eyes will be on the outer side of the front sponson's. When I make the rear airfoil the uprights will look like the rear fin of a shark. I just hope the light grey paint isn't going to be too hard to see 
Could be fun
Hurry up and earn the needed token's to move ahead with your own creations, it's awful lonely on here all by myself!