I've created a model which uses all the correct arma LODs. I've placed the p3d in my mpmission and spawned using:
createSimpleObject [getMissionPath "mymodel.p3d", AGLtoASL screenToWorld[0.5, 0.5]]
Model spawns in perfectly however after 5-10 minutes of the model being spawned in the mission, random players start being kicked for:
Wrong signature for file "mpmissions\__cur_mp.altis\mymodel.p3d"
I've spoken to Dwarden on discord and he forwarded me onto making a ticket since this could be an Arma issue. It would be awesome if we could get custom models working in mpmissions.