Great job Splint'... and also a great, comprehensive write up... many people, especially recipients, don't appreciate the amount of work that actually goes into it unless outlined... if you intend to sell, print this post and hang it on a board next to your gizmo... guaranteed to get quite a few extra shekels.
 
 So, what did I learn?

Don't do this!

..... but this beast took a lot of time and .....

Need to go back and rethink, be back soon with version #2!  

I could do all that in 1 step... buy it off Splinter!

That is why I backfill with Timbermate on MDF and just buff.  If I sold my stuff, not saying there's a great demand, but to recoup material and moreso labour, it'd be cheaper to but a 3 story solid brick house with a Lamborghini in the driveway or two... 2 Lambo's.

..... I used a slot cutter router bit to get this done.....

Incredible how some idiots (like me) can miss the obvious.  On boxes I've always routed the dado in the sides before glue up, which is a pain when dovetailing (I'm no hero, Leigh D4R is my hand(y) tool)... never considered this... on a square box it may require thinking at the closed end, however, worth a few brain storming.

If your first cut is too short... Take the second cut from the longer end... LBD