If you're looking into doing more extensive scripts than just overriding vanilla values or logic here and there, you'd probably enjoy a better development process than
1) start game
2) start campaign
3) wait 15 seconds to load
4) notice the script has ceased to run
5) go check metagame.log
6) resolve errors
7) go to step 1.

As most of the scripted gameplay elements in RWR are implemented as isolated "trackers", i.e. monitoring specific events received from the game/server, I regularly do tracker development directly in lobby map, in windowed mode. If it's e.g. something vehicle specific I'm doing, I set up lobby so that the vehicle is there (takes under a minute with inkscape), add my new tracker class in gamemode_tester.php, launch the game and say /_test_sp in chat in lobby map, which will run gamemode_tester.php.

If the tester script fails, it regularly does as programming errors just happen, I go check metagame.log what's the issue, correct it, and without leaving the game, again say /_test_sp in chat which will just restart the script. Works of course with other maps than lobby as well.

While that's fine for tracker components, dealing with the broader stuff can be tedious because of the 7 step cycle. There's another special command /_ssc, which can be useful if you want the script to restart as if it would've just loaded the match and would then begin doing stuff, without doing a map change. This removes steps 1-3 from the cycle when working inside a campaign. You'll probably need custom commands to help with development, and that's fine, you can do that, check the vanilla scripts, there are some examples there.

Another thing that can save you from plenty of back and forth is to use some real tools made for PHP programming, a syntax highlighter / validator is something you can't live without. I'm just barely coping with it by having Visual C++ do PHP highlighting and pre-running the scripts through some simple validation, while I know there would be better ways to save health and time. Anyway, it's great that in the end all you really need is Notepad to hack around with the scripts.