Tiplette No. 1:
Tack down some scraps of wood at right angles (into an
L-shape) onto a sacrificial surface (1/4" melamine) and
assemble your box against these scraps.
Tiplette No. 2:
Undersize your drawer bottom a smidge (smidges are found on
your tape/rule and are the smallest of ticks) so you can
pull the drawer square/aren't fighting the drawer bottom.
Tiplette No 3:
Dry fit your drawers (for the obvious reasons) and while the
whole works are still clamped together pre-finish the
interior(s) so that glue squeeze out pops out/off. Shellac
Onna Rag works good for this.
Tiplette No. 4:
Don't glue the bottom in. Wait for the box sides to set
(dry) and flip the whole thing over, re-check for square
(square up if needed) and run a bead of hot melt (that glue
gun you bought and never seem to use) around the rim of the
box. In fact, if you like you can make the groove a couple
of smidges (at least two of the smallest ticks) too wide,
flip the box over, weight down the drawer bottom (I prefer a
bag of lead shot for this) and fill the gap with the hot
melt. This leaves no gap on the show side.
Tiplette No. 4 might be a wee bit beyond the pale for some
who like to go around and feel up the bottoms of drawers so
you've really got to ask yourself, am I the type to go
around and feel up the bottoms of drawers?
Oh and the question has to be asked, when was the last time
you had to do maintenance on a drawer? Me? I'm thinking
should you ever have a drawer fail you'd probably be better
off re-making it, but then again, that's just me.