Then you can simply use an mSATA SSD for storage; format it appropriately as FAT32 with a GPT partition scheme (handy for a larger capacity drive) and you're set.
Booting off GPT system requires an updated bootloader, and one has not been created (much less tested) on the iHP-1xx/3xx family. Using GPT will also likely make the stock firmware unable to function (if you care about such things)
Also mSATA SSDs larger than 2TiB don't seem to be a thing yet. (At least not from reputable non-syllable-salad brands and in a form factor that will physically fit)
....So just stick to MBR for now.