Some pics of the ELT installation under the Selkirk floor in my old 170:

View with ELT installed:



View of ELT mounting, without ELT. Note the mounting plate spans two ribs...solid!:



View of ELT mounted in place:



I really liked this mounting. Keeps the ELT out of the way, well protected, and yet pretty easily accessable.

MTV

Thanks for all the ideas and suggestions on the ELT. We talked over all the options for the ELT with our AP/IA, who in turn talked with his guy at the FSDO. The general consensus was that mounting it to the sidewall with an approved framework (ac43.something) would be the best in our situation. Our 170 didn't have the structure under the floor like MTV's, and the deviation from the stc to put a door in the floor was looking like the the FSDO was going to require DER work on it. It's getting silly like that around here. Anyway, we also had to move it to the passenger sidewall instead of the pilots side due to a previous patch on that side from a battery access door that wasn't approved. Same FSDO, btw. Anyway, the extended baggage kit is in, the ELT is installed and doesn't flex at all. Next comes the seat recovering and then the weighing.