First and foremost, Your build looks great!
For the drip tray I decided to use heavy duty Velcro and can confirm that it easily supports several full beers with no challenge.
I just did a quick test with a full growler (just water in there for the test), and the drip tray was able to...
My wife insists I keep this SMaSH on tap:
12 lb Vienna malt
1 oz Amarillo (FWH)
1 oz Amarillo (15 min)
1 oz Amarillo (1 min)
Belgian Style Saison Ale Yeast Blend (White Labs #WLP568)
:mug:
Are you using a braid or manifold or .... ?
I have had similar challenges (low 70s) that I suspect are due in part to channeling issues / poor manifold design.
More aggressive stirring and longer mash times have helped a bit.
A friend of mine just made a prototype High Density...