@NotaReptile
Actually... In practice, a triangle design produces its own lift from forward motion, in other words, it acts as a lifting body. Therefore, the low volume is more than compensated for- in fact, rather than having a smaller payload, it's increased greatly. The Canadian "Solar Ships," for example, are hybrid solar-powered delta-shaped remote-resupply airships that are only 20 meters wide and long, yet carry 13,000 lbs of cargo(I'd show you a picture, but none fit on the page). That's six times as much as a De Havilland Beaver bushplane, yet at a fifth the cost.
The idea of a stealth blimp is still ridiculous, however. While it is somewhat possible for an airship to be stealthy- at least, some of the time- the facilities to HOUSE them and construct them certainly wouldn't be. Additionally, in order to have some sort of 24/7 stealth, you must satisfy a set of contradictory requirements: altitude, so you aren't seen, adaptive camouflage, which weighs a lot, and size. Even at 20,000 feet, a 300 foot airship is still visible, about the size of your thumbnail. But for a very complicated series of reasons that involve windspeeds, high-altitude airships can essentially stay at up to 20,000 feet OR at 70,000 feet, but not in between. To reach that higher altitude, you must explosively increase the size of the ship, and drastically cut the payload(but the payload is tied to the size, remember?), because Helium expands, fills out the hull, and simultaneously loses lift progressively with altitude.
TLDR; there is no way that you can counter the visibility problem. Blimps do fine in and of themselves inherently avoiding heat and radar signatures(smaller engines and fabric hulls are not conducive to either), but there's no way to make it not immediately apparent to anyone looking up.
