So I’ve been digging around a bit and actually found what looks like a full dump for the Sonim XP3800 (Verizon model) on XDA. Decided to give it a try through QFIL (Qualcomm Flash Image Loader).
I’m not really familiar with QFIL, so there’s a good chance I’m missing something basic here… but I tried flashing and got a “QSAHARA FAIL” error. 
I’ll upload the dump I found, in case anyone can confirm whether it’s good — or maybe share a known working one? Could really use a second opinion.
Still learning as I go here. Appreciate any help.
https://xdaforums.com/attachments/xp3800verizonfiles-zip.6155479/