There is useful information in this forum on offline Oruxmaps http://www.oruxmaps.com/, including http://bushwalk.com/forum%20viewtopic.php?f=21&t=23630, http://bushwalk.com/forum/viewtopic.php?f=21&t=24062&p=310421, http://bushwalk.com/forum/viewtopic.php?f=36&t=23130, QLD http://bushwalk.com/forum/viewtopic.php?f=38&t=21764&p=286919, NSW http://bushwalk.com/forum/viewtopic.php?f=21&t=21989, VIC http://bushwalk.com/forum/viewtopic.php?t=23800 and TAS http://bushwalk.com/forum/viewtopic.php?f=3&t=17091&p=228044.
If you have an Android 6 (Marshmallow) or later phone with limited internal memory, you may opt to access more memory by setting up a fast, high-capacity micro-SD card as emulated internal (= adoptable = flex) storage. There are trade-offs https://liliputing.com/2015/10/android-6-0-can-treat-sd-cards-as-internal-storage-at-a-cost.html, but short of rooting the phone (thus voiding the warranty) it is the only way to get apps like Oruxmaps with their data into the extra memory provided by the card. The most serious risks (loss of phone capability in the event of SD card failure) are managed by a thorough phone backup routine https://www.howtogeek.com/125375/how-to-create-a-full-android-phone-or-tablet-backup-without-rooting-or-unlocking-your-device.
Unfortunately, Oruxmaps (to version 7.0.12) is not completely seamless in use of emulated internal storage. But it can be worked around. Here is what I use on a ZTE A462 (=Telstra 4GX Plus) phone, following some leads in the Oruxmaps manual and forum including http://www.oruxmaps.com/foro/viewtopic.php?t=4286, http://www.oruxmaps.com/foro/viewtopic.php?t=4286, http://www.oruxmaps.com/foro/viewtopic.php?t=1887. On this phone I have set Oruxmaps to use emulated internal memory(SD), which can be done in phone Settings>App Manager or Storage.
Some of this I have also needed in Android 5 (Lollipop) on a Samsung tablet with a microSD card installed as regular (portable) memory.
Vector topo OpenAndroMaps http://www.openandromaps.org/en/downloads are available through the link in Oruxmaps> Maps> Switch Map> Offline> +> World> OpenAndroMaps. For Australia, you would click ‘Download maps’ then choose Oceania followed by your region of interest. But then clicking ‘+’ and using direct installation fails if Oruxmaps has been set to use emulated internal memory. It gives >Error! in the Android notification, after a long time downloading.
Raster topo WMS maps are available as detailed in previous posts linked above (thanks to ken333 and others). Some menus have changed slightly with Oruxmaps versions (e.g. Map Creator is now under Map Tools). You can use multiple <wms>...</wms> entries in your wms_services.xml file to have all the corresponding servers appear in the Oruxmaps WMS list. Note that Oruxmaps reads this wms_services.xml file from the old location (oruxmaps\mapfiles) not the new one (Android\data\com.orux.oruxmaps\files\mapfiles) needed for map downloads as described below. One possibility (now that you have plenty of Android memory) is to download (via WiFi) the areas of interest at several resolutions (called layers in Oruxmaps Map Creator) so that when they are zoomed out somewhat they still fill the screen, giving fewer annoying prompts to select alternative maps. You might try the highest few layers in any set. Caution: this can result in very big downloads, or exceed the download limit. There will likely be download errors after Oruxmaps is set to use emulated internal memory, unless the work-around below is used.
The problem is that after Oruxmaps is set to use emulated internal memory it can not use for this purpose its default map location at ...\emulated\0\oruxmaps\mapfiles. The work-around is to: (i) set up another folder at ...\sdcard\Android\data\com.orux.oruxmaps\files\mapfiles (ii) assign this new path for map files in Oruxmaps settings.
Once the Oruxmaps settings point to the correct new folder for mapfiles, direct installation into Oruxmaps works again. Alternatively, you can download the maps of interest to a computer (then unzip if necessary) and copy the .map (and .poi if interested) files into this new folder. If the downloaded maps do not appear automatically, refresh the offline map list in Oruxmaps.
For (i) I have used Windows File Explorer with the phone connected via USB in MTP mode (after driver installation); or the more Android-friendly MyPhoneExplorer http://www.fjsoft.at/en/. The paths look a bit different in these explorers, but it is not too hard to work out either way.
For (ii), I find it necessary (after clicking in Oruxmaps settings on the path to be altered) to start at Root, then work along the path by first clicking the required box (to get a blue tick) then clicking the folder to add it to the path and access the sub-folders. For the last folder in the path, just click the box for a tick (don’t add it to the path) then select OK. The Oruxmaps path set in these steps was Root/sdcard/Android/data/com.orux.oruxmaps/files/mapfiles or Root/storage/emulated/0/Android/data/com.orux.oruxmaps/files/mapfiles (these paths seem to be equivalent).
It is also necessary to put OpenAndroMaps rendertheme (or style) files (such as the Elevate-Elements theme http://www.openandromaps.org/en/manual/orux-installation-pc in a new ...\sdcard\Android\data\com.orux.oruxmaps\files\mapstyles folder and point the Oruxmaps Mapsforge settings there. (Android uses / where DOS uses \).
For hiking, I find the Elements - Hiking theme best with OpenAndroMaps. The offline vector maps have relatively smaller file size, so they are great for finding an area of interest before zooming in then swapping to an offline WMS raster topo map with more detail.
Offline WMS maps downloaded before all this still appear from their default location. But after setting Oruxmaps to use emulated internal memory, subsequently downloaded WMS maps and OpenAndroMaps must use the new location.
The same approach may be needed with other folders used by Oruxmaps for downloaded or SD-stored content (customwpts, dem, geocaches, tracklogs
etc.). I have not tried them all - so some may need the default location whereas others may need the new location. If Oruxmaps needs to write to a file
on SD, that file will almost certainly need to exist in a folder under ...\sdcard\Android\data\com.orux.oruxmaps\files\. Anyone interested can experiment and perhaps report back.