You are right, multistage2 simulates no aerodynamics, its only for pure tall rockets, very basicly. I tryed payloadmanager too, its hard to control the "complex", RCS works only at mothership-vessel, unlike the author sayed.
But i have another resolution, i use now a single spacecraft3-vessel with a fixed engine, attached with a 2nd invisible pure engine-vessel. You can decide wich engine should be the 2nd vessel. Steering of the complet system is all time possible from both vessels. I did this method very succesfull to add Hover engines to other ships in the past, like the starclipper. I used attachment-manager from orbithangar, one time attached the both vessels keep together forever, too if you restart the scenario. Now i can add very simple payloads from ground to ISS in the one same vessel and very important, i have sabre engine cross range after reentry, with possibility of landing abort and reapproach, a important main feature of the Skylon system!
There are only 2 small problems:
1. The sabre engine air shutter keeps open or close forever, in the case of what mesh you choosed. Solution=write a anim for the open/close air shutter operation
2. Orbiter "forgets" the masses of attached spacecraft3 doughter vessels, after leaving a scenario. When you restart the scenario, theres only the mass of the mother-vessel, you can see it wonderfull with "BurnTime-MFD" or "Object-info" from orbiter ingame-menu. When you try to use the 2nd engine, the ship would accelerate with 40-50 G like Enterprise!!!
Solution=clear all time the tank of the attached doughter engine vessel, before you leave a scenario. Save the fill level in your brain and add the fuel mass after reloading of the scenario manuel to the tank, then orbiter adds the correct mass to the main vessel too.
Ok a right DLL would be the best way, but my solution i find mutch better than your multistaged-Syklon-mesh-thrower :lol:.