Is it possible to have a swimming platform with infantry, tanks and buildings (turrets, barracks, armory) on it? And it is also possible to control this platform (forward, backward, turn left, turn right). I'm asking because I have an idea for a map: On the platform is only place for one barracks or some tanks. So you can rush with your swimming barracks from refinery to refinery or place some heavies on it for a surprise attack. Best part would be, if both platforms are near to each other. I see great naval battles! Plattform could look like this: http://www.hadel.net/autos/assets/2009/akt/akt_sl_ponton2005_lg1550_03.jpg
I doubt buildings and turrets. Infantry and tanks, yes. You can use a func_tanktrain(?) to move around with. I'm pretty sure you can play with thrusters too, as a friend of mine made a zeppelin with thrusters.
Easier solution is to put a flag with a spawn point on it. Don't think you can drop buildings on a moving platform though.
You can't, buildings don't parent to moving objects when you place them and can't be placed on dynamic geometry.
You could try to use a trigger to detect the building and tell it to parent itself to the moving object, but i can't tell for sure wether it can actually be parented, you can't do it under normal circumstances, that's for sure.
Swimming platforms with only infantry and tanks would also be great. But know I first have to learn how to make a map with hammer ...
you can parent the empires entities, I edited my fdg to make blimps that fly around and you can spawn in. I made a test map of this, you can go on nachos and rtv to it if your curious.
Physics platforms are not an option. I tried making an LCAC landing craft that could carry Brenodi vehicles and infantry. Both the vehicles and Infantry would get stuck inside of it when it bobbed up and down or turned. I tried turning it into a tracktrain too, but players and vehicles still got stuck. Edit: that was 2.12 though