I'm checking to make sure I've got what a tac missile launcher can be mounted on and asking additional questions.
1. Launch rails I'm sure are mounted on vehicles.
Could launch rails be on a field mount similar to a tube launcher?.
Personally, I see nothing wrong with it. There are modern examples that look an awful lot like rails on a towable mount. However ...
"Launch rails must be mounted on vehicles." (Striker Book 3, Design Sequence 9, section B1a)
Of course, you could try to get around it by designing a towable "vehicle", but tube launchers are better for the field mount anyway. They're heavier, but they only take one movement phase to load, while rails take two movement phases - and I suspect we'd end up losing any weight or cost savings and then some by the time we finished inventing that towed rail-launch vehicle, so that's pretty much a dead end.
2. Package launchers are single shot weapons that appear I can mount on a field mount and vehicles.
Can a package launcher be hand-held by somebody?
That's actually their best use, disposable 1-shot shoulder-fired missile launchers. From Striker Book 2:
"Rule 37: Tac Missile Launchers ... B. Package Launcher: A package launcher is a simple man-portable system that consists of the guidance package for the missile and the missile in a container. The missile container serves as a disposable launch tube. Once a missile is fired, the empty container is discarded and a new container may be linked to the guidance package. Linking a new container to the guidance package takes two movement phases."
They'd be a bit awkward as a vehicle-mounted system; you'd have to pull off and replace the package when reloading (a minimum of two movement phases). Faster to use a standard tube launcher (which only takes one movement phase to load).
However, we need to keep the weight down to something a soldier in the field can carry. Consider using Rule 42 (Encumbrance) and drawing on the weight of existing weapons as a rough guide. For example, the 9cm ATRL comes in at 9 kg, the laser rifle comes in at 12.8 kg with battery, and the heavy machine gun comes in at 15 kg, so that's probably getting close to the upper practical limit for what a soldier can carry onto the field.
A soldier in battle dress could carry a pretty impressive missile, but you'd have to give some thoughts to its dimensions at that point - the fact that he can carry a telephone pole does not mean it would be convenient for him to do so in battle.
3. Tube launchers can be on a field mount or mounted on a vehicle
Yup.
Note that you could design a man-portable field-mount tube launcher. You just have to make it light enough to be backpack-carried. No, it's not shoulder-fired - you'd have to set it up before use. It's not as efficient as a package launcher: there's that need to set it up, and you'd be badly constrained by the need to keep its weight manageable. However, there might be advantage in a small man-portable missile launcher that could be reloaded in one movement phase. Consider a TL 6 infantry force using little wire-guided 1 to 1.5 km range missiles with a 6 cm HEAP warhead to oppose an attacker in battle dress: you could kill a target at 1 km on a roll of 7+, where their roll is 10+ to 12+. Also useful for destroying thin-skinned vehicles at extreme range or putting an HE round through the firing port of an opposing bunker.
4. Magazine launchers can only be mounted on vehicles.
Yup.
