I would assume if it has to stay above the weather its wings would be very prone to breaking. However at a descent rate of 0.5m/s and a 40:1 glide ratio. Descending the ~20,000ft before hitting weather would mean 150 miles travelled before being at risk of breaking up.

And I don't think an ejectable RTG would go down well with the public, although passive guidance onto a radio source would work and guided munitions sit for potentially decades and have to remain workable.

I wonder how feasible it would be to produce an aerostat that can reach 70,000ft. The DHS(or DEA, the networks shifted hands a few times due to budget cuts, etc) is operating radar based systems with one tonne payloads at 15,000ft. They have a system wide 98% operational efficiency despite being subject to extreme weather.

Carrying on my RTG love, the thermal output of shorter half-life materials could easily out produce the BTUs produced by a hot air balloon burner (800w/kg of vehicle weight) as the space based RTGs can already approach this and have longevities in the centuries. So I wonder if a hot air aerostat would have a longer longevity than the current helium based ones.