UPDATE with a better solution
I wasn't quite happy with the previous solution. It was not finished enough and left the edge of the slideout floor exposed to tripping or damage.
Took a while to consider... Why not a piece of trim that provided the transition when the slideout is extended, then easily removable when it's time to travel? That's what I did.
Two 1x4s that are 'hollowed out' underneath (see picture) to go over the black rubber seal; one edge sits on the main floor, the other edge on the slideout floor. It has 4 screws to install/remove - takes less than 5 minutes.
The wife is very happy with the results - so I'm very happy with the results!
2012 Flagstaff 26 Super Light
2003 Toyota Tundra