How much / often do you get rain? One perk of growing on stumps is that the roots still pull moisture from deep for a while. I'm basing that statement on watching where wild oyster mushrooms thrive here in Texas. It gets dry here on the regular, even in the east side of the state, and I've noticed that the oysters prefer dead trees that are still connected to the root system.
Also, in noticing failed mushroom growing attempts around here, that started with the inoculation of logs; the problem is that everything dries out. So, whatever you do, make sure that you maintain wet humid conditions. I use wood shavings or sawdust in a plastic bucket with a lose fitting lid (the fun guys need oxygen and humidity). I am looking for a way to get around using the plastic buckets, but for now that's the easiest way. I'm thinking of making some pottery vessels and sealing the outside with glaze. Another thing to try is to bury your branches in dirt, hugelkulture style, to help hold some moisture in that wood. My Hugel bed recently fruited some wild ink-caps. I never inoculated those logs, but that's the plan for a future hugel-bed so hopefully I'll get lion's mane or something better than ink-caps. Maybe you can use a 55 steel drum to inoculate the branches and get your desired mycelium a head start 1st ...I'll report back once I've tried that.
Main thing is that for anyone in a dry-ish area ... you can't underestimate how much moisture and humidity you need to provide. I only grow shrooms in the cooler wetter half of the year.
