Most smuggling missions I've seen tend be be less than 20 T but you might get two or more at the same station, I did try one in the Beta with the Diamondback and it was capable of running silent for over 5 minutes without heat-sinks and that was a standard build not a low energy one (standard build around 23% low energy around 17%). In fact I saw a video on the forum recently with players using it for combat without shields and using low energy weapons (m-cannons etc) the other ships simply couldn't detect them on scanners, so it might be worth trying some armored bulkheads and no shields for a smuggling DB-S that'll also give you more cargo space.
Here's a DB-S build, the power dist can be disabled once you set the power balance
http://coriolis.io/outfit/diamondba...0202020224.IwkBlSpI.Aw1-kA==?bn=DB-S smuggler
Just tried the DB-S with no shields and it'll run at 17% heat even 14% if everything except the sensors, thrusters, life support and power plant is off, TBH it really doesn't need heat sinks for smuggling as I flew it out of a Coriolis in silent running until I was far enough away to jump,
I auto landed at an outpost in silent running (the pad was on the far side so worst case I reckon) and even without heat sinks the ship got up to 82%, I think there's more to be had from the DB-S, smaller power plant, power dist (if it's disabled once set you have the performance with no power draw).