Here's a basic installation checklist.

Download ALL the Latest Versions of the required Mikero tools.

• Arma3P
• ExtractPbo
• DeRap
• DePbo

Install the ArmA 3 Tools to whatever Steam Library you like (for example E:\SteamLibrary\SteamApps\common\Arma 3 Tools).

Do this by starting steam client, browse to Library → Tools → ArmA 3 Tools, then right mouse click them and choose Install Game. Now you only need to choose which library to install them and agree the license and so forth. Then just wait for steam to install the tools. Do not “opt for beta” because that downloads 22gb worth of bis sample models.

Next you need to replace the mapdisk.bat file which can be found on the root directory of the ArmA 3 tools, with your own. This is because the original mapdisk.bat supplied by the tools is not working properly.

Copy all this text for “mapdisk.bat” replacement.

set ArmAWorkPath=C:\ArmA3Work
set DriveLetter=P
 
@echo off
subst %DriveLetter%: /D
subst %DriveLetter%: "%ArmAWorkPath%"
 
NET FILE 1>NUL 2>NUL
if '%errorlevel%' == '0' (goto gotEscalation) else (goto getEscalation) 
 
:getEscalation
if '%1'=='ELEV' (shift & goto gotEscalation)  
setlocal DisableDelayedExpansion
set "batchPath=%~0"
setlocal EnableDelayedExpansion
echo Set UAC = CreateObject^("Shell.Application"^) > "%temp%\BIS_getEscalation.vbs" 
echo UAC.ShellExecute "!batchPath!", "ELEV", "", "runas", 1 >> "%temp%\BIS_getEscalation.vbs" 
"%temp%\BIS_getEscalation.vbs" 
exit /B 
 
:gotEscalation
setlocal & pushd .
subst %DriveLetter%: /D
subst %DriveLetter%: "%ArmAWorkPath%"

::--- clean & exit
del %temp%\BIS_getEscalation.vb
exit /B

Open text editor and paste it in there - save as (all files) Mapdisk.bat“ (Not “mapdisk.bat.txt”).

Open - Not Run - Mapdisk.bat and edit this line near the top of the file.

set ArmAWorkPath=C:\ArmA3Work

Change it to be Your Path to Your tools - eg:

set ArmAWorkPath="E:\SteamLibrary\SteamApps\common\Arma 3 Tools"

Look very carefully at that line… Notice how theres Spaces in that path? “Arma-space-3-space-Tools”.

DOS doesn't likes spaces! But they're OK if they're in “quotes” like you see above.

Once Mapdisk.bat is repathed and ready - navigate to your ArmA 3 Tools directory - you'll find there's a mapdisk.bat already - Rename that one to “mapdisk.bak” and drop your new, improved one in there instead.

Now - run that new Mapdisk.bat by doubleclicking it and your P:\ drive will appear - it will have the entire contents of your freshly installed ArmA 3 Tools directory in there already.

Run ArmA3P from Mikero, go make a coffee and wait… ArmA3P should run all the way - with No errors, and report success. This will take really long time, especially the dubbing pbo takes forever, be patient and wait.

Because Terrain Builder (TB) relies on a couple of registry keys, it's necessary to run TB once from the Steam Tools menu - so go to Steam, call up the ArmA 3 tools and doubleclick - choose “Launch Terrain Builder” and - once you see Terrain Builder open - just close it again and close Steam too - you're done with that.

From now on - forget where your ArmA 3 Tools actually are - from now on everything happens on P:\ !

And - that's it!

You should be good to go with no further fuss… When you want to run TB - always run it directly from the Terrain Builder directory on P:\ drive.

Never ever run Steam client → ArmA 3 Tools → Prepare virtual P: Drive, it will delete all your files in the P: drive if it already exists, this is very dangerous command, please be careful not to ever run it.