I've been having some problems that I did and didn't see mentioned in the thread this far, first off, the tech tree but then there are other issues... Firespitter is apparently not compatable with .25, and being a noob I have no clue what implications that has. There is no texture for the 1.25m Thermal engine (Its completely white), the Large Argon tank while physically occupying space appears extremely small, making for large awkward gaps. The thermal engines don't seem to work properly, as I can only switch them between Thermal vacuum (Which doesn't work) and monopropellant, which after an entire runway got me up to 26m/s. There is also no FX when the engine is on, so the mod is pretty much broken for me. Hoping for fixes and insight if I installed it wrong.
