They are 100% sealed... I like to be double sure its sealed. Most larger chest freezers come with a drain tube so you can utilize that in your design concept also so you can thaw the freezer & drain it without tipping the unit over which damages the freon
Interesting concept. What I would do is use that thermometer & stick it in the chest freezer where your nutes would be and if it climbed past a certain degree mark the unit would kick on... The other thing you need to take into account is these were designed to hold food not water. Water will be pushing against the sides so while your out looking push hard against the sides make sure it can actually hold the volume of water your after. I have filled up my 14Q before with bleach water so I know that model can hold the weight of the water. Your electrical sits right below the reservoir just another thing to be "worried" about
I see where your coming from, boy do i hate conversations in text, if we was all sitting in a cirlie this would be resolved in 5 minutes, well maybe not, seeing as we sitting in a circle i'm sure theres probably a cloud hovering above & in that case we would be discussing it for hours...lol
the hole in the bottom i would seal for starters, good old clear silicone, if its good enough for my 125 gallon fish tank its good for my res too,
also i'm not looking to hold too much water, 10, 15 gallon max, hence the smal 3.5 cu ft freezer, any bigger means more nutes, more money
that thermometer i thought was only for air, if it works in water would make a great safety shut on or off switch
the other part of the plan is to mount a small pump in bottom corner & run hose up & out, will serve to empty & fill
i'm still bouncing around with ideas, bounce yours back & we will all compare n learn
happy toking