My solution
After spending a lot of time thinking about ELT location, I have finally settled on a solution that seems to work for me. The thread above, as well as the instruction manual of the ELT really helped clarify my thinking. First of all, a couple premises that helped determine the location (and are just my own opinions):
1. I am a firm believer in the ELT being very accessible in case of pilot incapacitation. Even if, and especially because ELT's have a fabulously pathetic activation rate, I wanted to be able to reach it easily, even if I was hurt.
2. I did not want to put it under the baggage compartment for two reasons: (a) a lot of baggage may have to be moved to access it and all the screws in the floor removed. See point #1 above. (b) Some people have put access doors in their baggage floors, but everything I've heard from Van's (all secondhand, so take it for what it's worth) is that they are not real fired up about chopping up the floors like that.
3. 7/9's tend to be tail heavy. I wanted to keep the weight as far forward as possible.
4. The ELT manufacturer is very adamant that the mount not flex and that it be able to withstand 100# without deflection and 450# without tearing away from it's support. It points out that a lot of ELT's failing have to do with improper mounting (short aside: of course, the manufacture would say this to explain failures). The mount that Van's supplies may provide for the ELT's manufacturer's requirements, but it still seems very flimsy to me, and others have reported less than desirable rudder cable clearance. It also violates one of my basic premises in that the baggage area would have to be kicked in or screws removed. In that location, it also has a more negative effect on c.g.
So this is what I came up with...
It's located such that the seatback, when installed in it's aftmost position, will not touch the ELT or its antenna cord. It also takes into account the 17.5 degree angle of the floor, since the ELT must be placed within 10 degrees of the longitudinal axis of the plane.
However, by placing it at 0-degrees of angle relative to the plane, it had to be pushed back and overhang the flap actuator slightly to avoid the seatback. I made it so that there is 1/4" vertical distance between the bracket and the flap actuator. Since everything is fabricated from .063 stock it would take a LOT of weight to get it to even rub against the actuator. And even if it did rub, it would not cause that much of a problem. Still, I did leave enough of the platform extending out the back so that, if it does become necessary, I can support the platform aft of the flap actuator as well.
The only big downside of this location and arrangement is that I'll have to keep baggage off it. I tend to keep things tied down, so I'm not too concerned, but have been thinking about some other solutions to that problem as well. Anyway, I hope this help others trying to determine where to place theirs. I appreciate the input of everyone else's ideas on this thread.