Impressive! From what I know of Texas weather patterns, a yurt is an interesting choice. I've been told it can be 70 F one day, 30 F the next during the cool season...
I would suggest a professional (and warranted) vinyl cover--the sun there will eat up canvas pretty quickly, plus the torrential downpours would saturate it and make things rather cool on wet days (evaporative cooling), requiring
. If you have ready water access (unlikely for off-grid), you could use that to your advantage on hot days though. Canvas of course would require a
barrier; I think vinyl is normally waterproof, so any moisture barrier would be a redundant protection in case accidental puncture.
Insulation? Maybe a little, but it really depends on how well sealed you make everything. Yurts are often pretty drafty, which will steal/add more heat than you'd expect (season dependent). Also, what's your heating fuel budget?
Any idea on what you'll be doing for heat? Yurts being low thermal mass they'll cool quickly after the daytime high's...