To start the day, I matchdrilled and deburred the baggage floors

Next dimpled the nutplate ears on the inboard side baggage floors which serve as attach nutpaltes for the baggage tunnel cover.

Also dimpled the back side nutplate ears that attach to the F-705 bulkhead.

Once rivetted in place, the area underneath the baggage floors becomes hidden and unavailable. So better think now it you need to install something on the belly skin underneath that section such as antenna's, elt, etc...

In my case, I'm opting for the baggage area cut out like many other builders have been doing before me. My change from the plans is to install the ELT device underneatch the passenger side baggage floor. On the pilot side, I will also make a larger cutout as this area can be used for storage of oil bottle, small tools, etc. When you will be doing some loops and other acro stuff, you don't want oil bottles to float around in the plane and the area underneath the baggage floors is just big enough to hold to oil bottles. Ideal !

There isn't much documentation on this on the other sites so I decided to make it a long story with a lot of pictures describing in detail how I made my passenger side ELT cut-out.

Before making the cut out, I needed some dimensions to confirm that it would fit inside that inner bay of the baggage compartment.
I am planning for the ACK-406 ELT which you can find on the Spruce website here.

Dimensions and manual can be found on Spruce site. 7.75" long,2.85" width,2.85" height, 1.6 pounds in weight with battery.

The height is the biggest restriction on install options. The forward side of the baggage bay is higher than the back end so I opted to install the ELT on the side forward of the floor.

I started drawing first the side lines on the baggage floor where the F-727 and F-726 baggage ribs are located.
In the middle of those two lines I made a center line drawing and used that to center a 4.75" inch width line. The length is 9.6".
Then I made a center point to draw 3/4" radius in the corners. First made some pilot holes for the unibit step drill to get grip.

 Then I used the unibit to cut the 3/4" inch holes

I taped the baggage floor with some painters tape because I used a electric jigsaw to make the cuts. In the bottom picture, the inboard one is finished and ready for the cut on the outboard side.

Then used the vixen file and deburr wheel on the grinder to finish it off.

The cover is made out of some 0.025" stock. The cover overlaps the cutout by about 0.8" on all side.
When finished, I made center lines on the cover and on the floors so that I could align those lines to draw the contours on the baggage floors as in the picture below.

 the allows me to draw center lines between the edges of the compartment cut-out and the cover countours.
This is where the nutplates will be located I decided to use K1100-08 countersunk screw nutlplates to attach the cover.
With these dimension, you will need three screw on each side.

And now it's really simple, you have the centerlines still on your parts, slide the cover underneath the floor and re-align the cover centerlines with the ones on the baggage floor. Calmp in place and drill the holes #19 for the AN509-8R8 screws

Once the holes are made, I installed a nutplate using a screw with a lot of washers to locate the hole and use the nutplate ears as template to drill the ears.

All nutplates drilled.

Then dimpled the nutplate ears #40 and screw location #8 and rivetted the nutplates on the baggage floor.
Et voila, you have yourself a compartment in the baggage floors.