About a month ago, when my playthrough finally allowed me to enter Solstheim (I usually like to complete the game in this order: vanilla, Dawnguard and Dragonborn), at first everything was okay and then I began to experience an unusually large amounts of CTDs in almost every place on the island.

At first it must be my gamesave that had a problem, did cleaned them and even then the CTDs persisted. 

I then tried to debug ModOrganizer logs, attempting to track down which was causing what CTD, using a system of elimination to nail the culprit, forcing to remove every other mod -- whether it's textures, meshes, scripted mods, etc. -- I though were okay back on mainland Skyrim. But still the problem couldn't go away.

Heck, even downgrading USKP and associated patches didn't work. So I was in a quandry, until I came across this STEP thread discussing about memory management: link

It was a revelation -- turned out that although I had the memory patch configured in SKSE.ini it wasn't enabled properly and hence I got the CTD plague. Based on those findings in the STEP thread, here is what I think should resolve problems:

enblocal.ini, under [MEMORY]:

ExpandSystemMemoryX64=false (if using SKSE 1.7.1 using Sheson's memory patch)
ReservedMemorySizeMb=64 (if you have 2gb of VRAM, 128 to 256 if using 1gb VRAM)
VideoMemorySizeMb=896 (subtract 128mb from your total VRAM, as that should be reserved for Windows Aero. Not sure about those using SLI or Xfire setups.)
EnableCompression=true (optional, should be if you need to cram in more textures)
AutodetectVideoMemorySize=false

Check also if you have vsync enabled in the same enblocal.ini

skse.ini, under [MEMORY]

DefaultHeapInitialAllocMB=768
ScrapHeapSizeMB=256

And make sure that MO has configured skse_loader.exe to have the switch -forcesteamloader included, so that Sheson's patch kicks in.

Using these has somehow given my playthrough a breath of fresh air, adding more FPS, especially when roaming in Solstheim.